Checklist
Client onboarding checklist for accounting firms.
Your firm's onboarding steps, from engagement letter to HMRC authorisation, and the documents to ask each type of client for.
Last updated · Facts checked
A client onboarding checklist for an accounting firm has two halves. One is your own work: the engagement letter, the anti-money laundering checks, the letter to the previous accountant, HMRC authorisation and setting the client up in your systems. The other is the documents you need from the client to do all of that.
This guide covers both. Part 1 explains your firm's steps and links the official guidance for each. Part 2 lists the documents to request, for an individual, a sole trader, a limited company and a partnership, with a "why we ask" line you can paste into your request.
Client onboarding at a glance
The order varies from firm to firm, but most new clients go through these five steps before the real work starts.
- Engagement letter. Agree the scope, fees and responsibilities in writing.
- Customer due diligence. Identify the client, and anyone who owns or controls them, under the anti-money laundering rules.
- Professional enquiry. Write to the previous accountant, with the client's permission.
- HMRC agent authorisation. Get the client's authority to deal with HMRC for each tax you'll handle.
- Set up the client in your systems. The client record, deadlines, a privacy notice and the documents they owe you.
Most of these steps need something from the client: a document, a fact or a permission. That's why it pays to ask for everything in one request, on the day the client says yes.
Part 1: your firm's onboarding steps
These steps are yours. They depend on your professional body, your supervisor and your own procedures, so treat this as a map, not a rulebook. The sources are listed at the end of this guide.
1. Agree the engagement letter
An engagement letter sets out what you'll do, what the client will do and what it costs. It protects both sides when a deadline is missed or a job turns out bigger than expected.
- Use your body's sample wording. ICAEW publishes sample engagement letters for individuals, partnerships and companies, with schedules for each service.
- Tailor it. ICAEW calls its helpsheet best practice, not a professional standard, and expects you to adapt the wording to each engagement.
- Include a privacy notice. ICAEW's helpsheet has a part for this, and you need one anyway (see step 5).
2. Carry out customer due diligence
If your firm is covered by the Money Laundering Regulations, you must check that a new client is who they say they are before the relationship starts. HMRC's guidance says this means getting their name, a photo on an official document, and their address and date of birth.
- For a business, you also identify the beneficial owners: the people who own or control it.
- Ask about the relationship. The guidance includes its purpose and intended nature, such as the client's business and where their money comes from.
- Check higher-risk clients more closely. Enhanced due diligence applies in some cases, such as a politically exposed person.
- Keep the records. HMRC's guidance says you keep due diligence records for 5 years from the end of the business relationship.
The accountancy sector's own guidance, AMLGAS, is published by CCAB and adopted by the accountancy supervisory bodies. Your supervisor's rules come first.
Collecting a document isn't checking it
A passport photo in your inbox, or in any upload tool, isn't due diligence on its own. Checking it, recording what you checked and assessing the risk is the part the rules care about.
3. Write to the previous accountant
Most accountants call this "professional clearance". ICAEW's helpsheet calls it professional enquiry, and points out that the previous accountant can't give or withhold permission for you to act. The decision is yours.
- Ask the client first. You need their permission to contact the previous accountant, preferably in writing, and the previous accountant needs it to reply.
- Write to the previous accountant. Ask whether there's anything that should affect your decision to accept the work.
- Chase if you hear nothing. ICAEW's helpsheet describes what to do when there's no reply, including a final letter giving a reasonable deadline.
Ask the client for their previous accountant's details and permission at the same time as their documents. Handover papers from the previous accountant then usually follow.
4. Get HMRC agent authorisation
You can't deal with HMRC for a client until they've authorised you, and the method depends on the tax. HMRC also says plainly that you shouldn't use your client's own HMRC sign-in.
| Tax | How HMRC says to get authorised |
|---|---|
| Self Assessment | Online Agent Authorisation, or form 64-8 |
| Corporation Tax | Online Agent Authorisation, or form 64-8 |
| PAYE | Online Agent Authorisation, the client's business tax account, or form 64-8 |
| VAT | The digital handshake in your agent services account |
| Making Tax Digital for Income Tax | The digital handshake, or adding existing Self Assessment authorisations |
With Online Agent Authorisation, HMRC posts the client a letter with a code within 7 working days. The client tells you the code, usually within 30 days, and there's one code for each tax. Tell clients the letter is coming, and ask for the code as soon as it arrives.
5. Set up the client in your systems
The last step turns a signed letter into a working client.
- Create the client record with the right type: individual, sole trader, limited company or partnership.
- Add their deadlines: tax returns, accounts, VAT quarters and payroll dates.
- Give them your privacy notice. The ICO says people must get privacy information when you collect their personal data, including your retention periods.
- Decide where their documents live, and how long you keep each kind.
- Note what's still outstanding, so nothing from onboarding is forgotten once the work starts.
Part 2: documents to request from the client
The lists below are typical examples to tailor to each client, not a list of what you're required to collect. Your due diligence procedures decide which identity documents you accept and how you check them.
Before you send a list:
- Remove what doesn't apply. No staff, no payroll. Not VAT registered, no VAT certificate.
- Name the acceptable documents. "A passport or photocard driving licence" beats "photo ID".
- Ask for facts as facts. A Unique Taxpayer Reference is one line of text, not a document to scan.
- Ask once. One list on day one is quicker than five emails over a month.
Individual
For a client who needs a personal tax return but has no business.
| Document | Why we ask |
|---|---|
| Photo ID, such as a passport or photocard driving licence | To confirm who you are, as anti-money laundering rules require. |
| Proof of address, such as a recent bank statement or utility bill | To confirm where you live. |
| Your Unique Taxpayer Reference (if you have one) | So we can find your tax record with HMRC. |
| Your National Insurance number | HMRC uses it to identify you. |
| Your last tax return and tax calculation (if you've filed one) | Our starting point for this year. |
| Recent letters from HMRC (if any) | So we know about anything HMRC has asked for or changed. |
| Your previous accountant's name and contact details (if you had one) | So we can write to them, as our professional rules expect. |
| Your written permission for us to contact your previous accountant (if you had one) | They can't reply to us without it. |
| The HMRC authorisation code, once HMRC's letter arrives | So we can deal with HMRC for you. |
Sole trader
Everything an individual sends, plus the business.
| Document | Why we ask |
|---|---|
| Photo ID, such as a passport or photocard driving licence | To confirm who you are, as anti-money laundering rules require. |
| Proof of address, such as a recent bank statement or utility bill | To confirm where you live. |
| Your Unique Taxpayer Reference | So we can find your tax record with HMRC. |
| Your National Insurance number | HMRC uses it to identify you. |
| A short description of the business, with its trading name and start date | To understand the work, and the risks, we're taking on. |
| Your last tax return and tax calculation | Our starting point for this year. |
| Your last year's accounts (if your previous accountant prepared them) | Our opening figures come from last year. |
| Which bookkeeping software you use (if any) | So we can arrange access to your records. |
| VAT registration certificate (if you're VAT registered) | To take on your VAT returns. |
| PAYE reference and latest payroll reports (if you employ anyone) | To take on your payroll. |
| Recent letters from HMRC (if any) | So we know about anything HMRC has asked for or changed. |
| Your previous accountant's name and contact details (if you had one) | So we can write to them, as our professional rules expect. |
| Your written permission for us to contact your previous accountant (if you had one) | They can't reply to us without it. |
| The HMRC authorisation code, once HMRC's letter arrives | So we can deal with HMRC for you. |
Limited company
For a small private limited company. The company is the client, so identity documents come from the people behind it.
| Document | Why we ask |
|---|---|
| Company number | So we can find the company at Companies House. |
| Certificate of incorporation | To confirm the company exists and its registered details. |
| Articles of association (if they aren't the standard model articles) | Some decisions depend on them. |
| A list of shareholders and their shareholdings | To identify who owns the company. |
| Photo ID and proof of address for each director | To confirm who runs the company, as anti-money laundering rules require. |
| Photo ID and proof of address for anyone with more than 25% of the shares or votes (if they aren't directors) | To confirm who owns or controls the company. |
| A short description of the business | To understand the work, and the risks, we're taking on. |
| The company's last accounts and Company Tax Return | Our opening figures come from last year. |
| The company's Corporation Tax Unique Taxpayer Reference | So we can find the company's tax record with HMRC. |
| VAT registration certificate (if VAT registered) | To take on the VAT returns. |
| PAYE reference and latest payroll reports (if the company runs a payroll) | To take on the payroll. |
| Each director's Companies House personal code (if we'll file for the company) | Directors give it in the company's next confirmation statement. |
| Recent letters from HMRC or Companies House (if any) | So we know about anything outstanding. |
| The previous accountant's name and contact details (if the company had one) | So we can write to them, as our professional rules expect. |
| Written permission for us to contact the previous accountant (if the company had one) | They can't reply to us without it. |
| The HMRC authorisation code, once HMRC's letter arrives | So we can deal with HMRC for the company. |
The 25% line is how GOV.UK usually defines a person with significant control. Your procedures may set a different test for beneficial owners, so follow those.
Partnership
For an ordinary business partnership. Send the request to the nominated partner, and ask them to collect each partner's documents.
| Document | Why we ask |
|---|---|
| Photo ID and proof of address for each partner | To confirm who runs the partnership, as anti-money laundering rules require. |
| The partnership agreement (if there is one) | It sets how profits are shared and who decides what. |
| The partnership's Unique Taxpayer Reference | So we can find the partnership's tax record with HMRC. |
| The name of the nominated partner | They deal with HMRC for the partnership. |
| Each partner's Unique Taxpayer Reference and National Insurance number (if we'll do their own returns too) | So we can find each partner's tax record. |
| A short description of the business | To understand the work, and the risks, we're taking on. |
| The last Partnership Tax Return and accounts | Our opening figures come from last year. |
| VAT registration certificate (if VAT registered) | To take on the VAT returns. |
| PAYE reference and latest payroll reports (if you employ anyone) | To take on the payroll. |
| Recent letters from HMRC (if any) | So we know about anything outstanding. |
| The previous accountant's name and contact details (if you had one) | So we can write to them, as our professional rules expect. |
| Written permission for us to contact the previous accountant (if you had one) | They can't reply to us without it. |
| The HMRC authorisation code, once HMRC's letter arrives | So we can deal with HMRC for the partnership. |
Copy the lists
NEW CLIENT ONBOARDING: DOCUMENTS
Remove what doesn't apply before you send.
IDENTITY (every client type)
- Photo ID, such as a passport or photocard driving licence
For a company: each director, and anyone with over 25% of the
shares or votes
For a partnership: each partner
Why we ask: to confirm who you are, as anti-money laundering
rules require.
- Proof of address, such as a recent bank statement or utility bill
Why we ask: to confirm where you live.
TAX REFERENCES
- Unique Taxpayer Reference (personal, company or partnership)
Why we ask: so we can find your tax record with HMRC.
- National Insurance number (individuals, sole traders, partners)
Why we ask: HMRC uses it to identify you.
THE BUSINESS (sole traders, companies, partnerships)
- A short description of the business, with its trading name and
start date
Why we ask: to understand the work, and the risks, we're taking on.
- Company only: company number, certificate of incorporation, a
list of shareholders, and the articles if they aren't standard
Why we ask: to confirm the company and who owns it.
- Partnership only: the partnership agreement and the name of the
nominated partner
Why we ask: it sets how profits are shared and who deals with HMRC.
- Which bookkeeping software you use (if any)
Why we ask: so we can arrange access to your records.
LAST YEAR
- Last tax return and tax calculation, or last accounts and
Company Tax Return
Why we ask: our opening figures come from last year.
- Recent letters from HMRC or Companies House (if any)
Why we ask: so we know about anything outstanding.
IF IT APPLIES
- VAT registration certificate
Why we ask: to take on your VAT returns.
- PAYE reference and latest payroll reports
Why we ask: to take on your payroll.
- Each director's Companies House personal code (if we'll file for
the company)
Why we ask: directors give it in the next confirmation statement.
YOUR PREVIOUS ACCOUNTANT
- Their name and contact details
Why we ask: so we can write to them, as our professional rules
expect.
- Your written permission for us to contact them
Why we ask: they can't reply to us without it.
HMRC
- The authorisation code from HMRC's letter, once it arrives
Why we ask: so we can deal with HMRC for you.
Sending it
Send the list on the day the client says yes, alongside the engagement letter. Everything in Part 1 waits on something in Part 2, so a slow start here delays the first piece of real work.
- Give a due date. Two weeks is enough for most onboarding lists. Allow for the HMRC letter, which can take 7 working days to arrive.
- Explain the ID request. New clients sometimes find it odd. One line saying the law requires it saves a phone call.
- Chase only what's missing. A reminder that names the two items still outstanding works better than a general nudge.
For timings, see how often to send reminder emails to clients. For the wording of the first email, see the document request email templates.
How to do this in GarnerDocs
GarnerDocs handles one part of onboarding: collecting the documents and facts in Part 2.
- One template per client type. Save the four lists above as templates, then start each new client's request from the one that fits.
- Facts as short answers. Set the Unique Taxpayer Reference, National Insurance number and HMRC authorisation code as short answers, so your client types them instead of scanning a letter.
- One private link. Your client uploads from a phone or computer with no account, and comes back to the same link when the HMRC letter arrives.
- Replacements for blurred photos. Ask for a new photo with a note your client sees next to that document.
- Reminders for what's missing. They list only the outstanding items, and stop once everything is in.
- Download, then let it go. Files are deleted after the retention period you choose, at most a year. Download what your procedures say you must keep for longer, such as due diligence records.
GarnerDocs doesn't do the rest of Part 1. It doesn't verify identity, run AML checks or keep your due diligence records. It doesn't send engagement letters or collect signatures, and it doesn't contact HMRC or the previous accountant for you.
Sources
- Your responsibilities under money laundering supervision, GOV.UK (HMRC). Checked on 21 October 2026.
- Anti-Money Laundering and Counter-Terrorist Financing Guidance for the Accountancy Sector 2026, CCAB. Checked on 21 October 2026.
- Change of professional appointment: incoming accountant, ICAEW. Checked on 21 October 2026.
- Engagement letters and privacy notices, ICAEW. Checked on 21 October 2026.
- How to get authorised to act as a tax agent on behalf of your clients, GOV.UK (HMRC). Checked on 21 October 2026.
- How to use the Online Agent Authorisation to get authorised as a tax agent, GOV.UK (HMRC). Checked on 21 October 2026.
- Verifying your identity for Companies House, GOV.UK (Companies House). Checked on 21 October 2026.
- People with significant control (PSCs), GOV.UK (Companies House). Checked on 21 October 2026.
- The right to be informed, ICO. Checked on 21 October 2026.
This guide is general information, not legal or tax advice. Your professional body and your anti-money laundering supervisor set the rules that apply to your firm.
Questions
What should a client onboarding checklist include?
Two things: your firm's own steps (engagement letter, customer due diligence, a letter to the previous accountant, HMRC authorisation and setting up the client) and the documents you need from the client to do them.
Can the previous accountant refuse professional clearance?
ICAEW's guidance says no: the previous accountant can't give or withhold permission for you to act. You write to them to find out whether anything should affect your decision, and the decision is yours.
Is a photo of a passport enough for customer due diligence?
Not on its own. Collecting a document is the first step. Checking it, recording what you checked and assessing the risk is what your supervisor will look for. Follow your own procedures and your supervisor's guidance.
How long does HMRC agent authorisation take?
With Online Agent Authorisation, HMRC posts your client a code within 7 working days, and the client has about 30 days to pass it on. VAT and Making Tax Digital for Income Tax use the digital handshake instead.