What the guidance requires
The PCRT AI guidance asks members to regard AI output as if prepared by a less experienced junior colleague and review it with appropriate scepticism. It says members remain accountable for the work whether or not AI was involved, and should be able to explain how a conclusion was reached and point to the source (PCRT AI topical guidance, January 2026). ICAEW's article of 7 September 2026 says to check every technical claim against a trusted source (ICAEW, using AI with confidence).
A review method
Record what was asked
Keep the prompt, the input files and the tool and version used. The PCRT guidance suggests keeping prompts and copies of the web pages relied on as part of the audit trail (PCRT AI topical guidance).
Source every figure
Trace each number in the output to a document, the ledger or an official page. A number with no source is removed or replaced with one that has a source.
Check every rule and rate
Look up each rate, threshold, date and rule on GOV.UK, legislation.gov.uk, an HMRC manual or a professional body, for the right tax year. Tools can rely on out-of-date material.
Re-perform the calculations
Recalculate totals, tax, VAT, percentages and any apportionment yourself, in a spreadsheet or by hand. A tool that writes text can produce sums that look right and are not.
Agree to the ledger
Compare the output with the trial balance, the bank reconciliation, the VAT return and last year's figures. Every difference is explained.
Check citations exist
Open every case, section and manual page cited. The PCRT guidance refers to Harber v HMRC [2023] UKFTT 1007 (TC) as a reason to confirm that cited case law exists (PCRT AI topical guidance).
Read it as the client will
Check facts about the client, tone and confidentiality. Remove anything about other clients.
Sign off
The reviewer records who reviewed, when, what was checked and what was changed.
A worked example
For example, a tool summarises a sole trader's year and states turnover of £48,200, expenses of £11,750 and a profit of £36,950, and says the trading allowance could be claimed. The reviewer agrees the turnover and expenses to the trial balance and finds expenses of £12,150, because a bank line was missed. The profit is recalculated as £36,050. The reviewer then checks the trading allowance on GOV.UK: it is up to £1,000 a year, and a person who claims it cannot deduct other expenses. Deducting £12,150 of real expenses gives the lower profit, so the tool's suggestion is wrong for this client. The summary is corrected, and the file records the change and the sources. See trading and property allowances.
Signs that output needs a closer look
- A rate or threshold with no year attached.
- A reference to a case, section or HMRC manual page that the reviewer has not seen before.
- Figures that total to round numbers, or that do not foot.
- Confident wording about a point where the law is uncertain. The PCRT guidance says material uncertainty should be disclosed to the client (PCRT AI topical guidance).
- Advice that looks generic, or that suggests an arrangement the client did not ask about.
- Facts about the client that do not match the file.
Automation bias
The PCRT guidance describes automation bias as the tendency to favour output from automated systems even when other information raises doubts about it (PCRT AI topical guidance). ICAEW's guide makes the same point about over-reliance (ICAEW: generative AI and ethics). A review that starts from the source documents, and comes to the output afterwards, reduces the pull of a confident answer.
Tools that file
The PCRT guidance covers tax software that can prepare and submit a return and can be set to make human review optional. It asks members to understand which steps are automated and to make sure the data and the draft submission can be reviewed before submission (PCRT AI topical guidance). Keep the review step switched on for every client.
Questions
How much of the output needs checking?
The PCRT guidance says due diligence on output can follow a risk-based approach (PCRT AI topical guidance). Anything that goes to a client or to HMRC, and every figure in it, is high risk. Internal working notes can be checked less fully.
What if a client sends figures produced by an AI tool?
The PCRT guidance says to apply due care and scepticism to data a client may have produced with AI, and to consider whether it is reasonable for the client's circumstances (PCRT AI topical guidance). Ask for the underlying records.
In Accountin
In Accountin, each VAT box keeps the transactions behind it, and reports run from the same ledger, so a reviewer can trace a figure back to its entries.
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