The Engagement Letter Gap: What MTD, ACSP Work and AI Left Out of Your Client Files

There is no deadline attached to this one. No HMRC countdown, no Companies House cut off, no penalty regime. That is precisely why it keeps slipping, and precisely why it is worth ninety minutes of partner time this month.

Most UK practices are carrying client files that describe a business they no longer run. The letters were written for annual accounts, a tax return, a VAT return and some payroll. Since then the firm has started submitting quarterly updates, verifying identities as an Authorised Corporate Service Provider, chasing digital records it never previously touched, and quietly running client data through AI assisted tools. The service has changed. In a great many files, the paperwork has not.

Why October 2026 Is the Right Moment

The timing argument is simple. Between now and February your capacity disappears. The Autumn Budget arrives on the 28th of October, the Companies House identity verification transition closes on the 18th of November, December year ends land, and then January swallows everything. After that you are into the April 2027 MTD cohort, mandatory payrolling of benefits in kind, and a fresh wave of onboarding.

If letters are not refreshed before the busy season, they will be refreshed in the middle of a dispute instead. That is the expensive version. A scope argument in late January, when a client insists that bookkeeping clean up, quarterly submissions and penalty appeals were all included in the original fee, is an argument you cannot win with a 2023 letter.

What Actually Changed in the Templates

The ICAEW engagement letter templates were fully reviewed and updated in March 2026, the first complete review since May 2023. The joint professional body schedule for MTD for Income Tax was also updated in March 2026. If your standard pack was built on the 2023 wording, you are missing four meaningful additions.

• Identity verification and ACSP services. New schedules exist for firms acting as Authorised Corporate Service Providers, setting out the scope of the verification service, what the firm is responsible for, what the client must provide, and the fees and limitations that apply.
• Filing accounts on behalf of clients. With Companies House reform moving filing towards software and tightening who may file, the updated schedules allocate responsibility for authentication codes, define the firm's role in submission, and make clear how far the firm is relying on client supplied information.
• MTD services. New schedules spell out which MTD services the firm provides, what digital records the client is obliged to keep, and the firm's dependence on third party software and other agents.
• Agreed upon procedures. Where a firm performs procedures without giving assurance, the letter should say so explicitly, list the procedures, and restrict who may rely on the output.

Separately, the Terms of Business were updated to deal with the use of artificial intelligence in service delivery, including whether AI tools are used, their limitations, and responsibilities around confidentiality, data protection and due diligence on technology providers. Insurers have already started asking about this at renewal. Clients will start asking too.

The Five Gaps We See Most Often

• Silence on quarterly updates. The letter covers a tax return. It says nothing about four quarterly submissions, who presses submit, what happens if the client sends records on the 6th of August, or who carries the cost of a late update.
• No scope exclusions. In scope services are listed. What is deliberately excluded is not. Bookkeeping remediation, digital record keeping, penalty appeals, HMRC enquiry support and software training are the usual casualties.
• No limitation of liability. Without a limitation clause the firm's exposure is effectively uncapped. The clause does not protect a negligent firm. It protects a firm that did the job properly from a claim driven by losses it did not cause.
• Nothing on identity verification or ACSP work. Firms are now performing a regulated verification function, often without a single line of paperwork describing it.
• No disengagement terms. Notice periods, final deliverables, handover of records and the fee position on exit are all absent, which makes removing a loss making client slow and awkward.

A Four Week Re-Papering Plan

You do not need to re-paper every client before January. You need to re-paper the ones that carry risk.

• Week one, triage. Pull a client list and tag every client whose services changed in 2026. MTD clients, clients where you handle Companies House filings or verification, payroll clients, and anyone whose fee has grown without a new letter. That tagged group is your priority population.
• Week two, rebuild the pack. Take the current professional body templates and build one firm standard pack with the new schedules bolted on. Add your AI wording to the Terms of Business once, centrally, rather than letting each manager improvise.
• Week three, price while you paper. A re-paper exercise is the only moment when a fee conversation feels natural rather than opportunistic. If quarterly updates have added a dozen touchpoints a year, the new letter should carry the new fee and, ideally, a monthly payment arrangement.
• Week four, send and chase. Issue in batches by client type, with electronic signature and a short covering note explaining what changed and why. Track signature status as a workflow, not an inbox. A letter that is sent but unsigned offers very little protection.

Make the Covering Note Do Some Work

Clients rarely read engagement letters, so put the message in the email. Three short paragraphs are enough. What has changed in the rules this year. What your firm will now do, and by when you need their records. What they are responsible for, including keeping digital records and responding to information requests. Clients who understand the bargain complain less in January.

The Commercial Upside

Firms treat this as defensive housekeeping. In practice it is one of the highest return exercises available to a practice this quarter. Clean scope reduces write offs, because work outside the letter gets priced rather than absorbed. Clear client obligations reduce the chasing that destroys margins between October and January. Documented AI and data terms make professional indemnity renewal conversations shorter. Workable disengagement terms let you exit the handful of clients who consume disproportionate capacity before the busiest weeks of the year.

There is a cultural benefit too. A team that knows exactly what is in scope says no with confidence. A team working from 2023 paperwork says yes to everything and then absorbs it.

Where Your Software Should Help

This is a volume job, so it should run on systems rather than goodwill. In TaxCalc, your client records and work management give you the data to triage quickly, identify which clients hold which services, and track progress as a job with owners and due dates. Document storage and electronic signature keep the signed versions attached to the right client, retrievable in seconds if a complaint or claim arrives in two years. Engager users can push the same exercise through structured workflows so that nothing sits half finished in a manager's drafts folder.

The principle matters more than the toolset. If you cannot answer the question which clients have a signed, current letter covering every service we actually perform in under five minutes, that is the real finding of this exercise.

The Bottom Line

Everything else on your compliance calendar this autumn has a date attached, which is why it gets done. Engagement letters have no date, which is why they get postponed until they matter most and cost most. The templates were overhauled in March 2026 for good reasons. The services your firm delivers in 2026 look nothing like the services your 2023 letters describe.

Block out an afternoon, triage the client list, and send the first batch before the Budget. It is the cheapest risk reduction available to your practice this quarter, and the only one that also puts fees up.