Through seven mechanical tests run on every payslip submitted, each targeting what a real payroll system leaves behind that a fabricated document cannot reproduce. 2026/27 figures below come from HMRC's rates and thresholds for employers[1].
The seven flags lenders check on every payslip
Failing one moves the file from desk-based approve to manual review; two or more route to fraud-team referral.
- PAYE arithmetic that does not match HMRC tables. Re-run the calculation for the declared tax code and pay period. Real payroll software hits the figure to the penny; fakes round or skip the cumulative year-to-date logic.
- NI category mismatch with the employee profile. Category letters[4] encode the rules: under-21 = M, apprentices under 25 = H, employees over State Pension age = C. A 19-year-old on Category A or a 67-year-old still paying employee NI is a flag.
- Pension deduction off the auto-enrolment band. Under the Pensions Act 2008[2], 2026/27 qualifying earnings sit between £6,240 and £50,270 with a minimum 8% total contribution (3% employer + 5% employee). A deduction that does not fit a plausible scheme rule refers.
- Year-to-date figures that do not reconcile across three payslips. Sum the period figures for the three most recent payslips and compare to the latest displayed YTD. Real software gets it right by construction; fakes drift beyond rounding error.
- Invalid employer PAYE reference format. HMRC references[3] follow `NNN/SUFFIX`. Format failures do not exist in the register; large lenders also match against it via specialist data providers.
- Net pay that does not reconcile. Net = gross minus all deductions (PAYE, NI, student loan, pension, anything else). Editing the gross without recomputing deductions is the most commonly failed test on template fakes; a 30-second calculator pass catches it.
- AI-generated typesetting tells. Uniform line-height and kerning across statutory and bespoke deduction lines, JPEG artefacts from screen-captured raster output, and stale tax codes or Scottish bands give away AI-generated fakes that pass the visual test but fail the typesetting one.
Why these checks now catch fakes that passed five years ago
Mortgage application fraud is rising; lenders have responded by automating these checks per the CIFAS Fraudscape report[5] and the FCA Financial Crime Guide[6]. A fabricated payslip now triggers referral before a human underwriter opens the file. The cost: rejected application, CIFAS marker for six years, possible Fraud Act 2006 prosecution. Legitimate routes to a missing payslip exist: an employer reprint, an HMRC Statement of Earnings via the replacement P60 guide, or an SA302 for self-employed income.
Primary sources
- 1.Rates and thresholds for employers 2026 to 2027 — gov.uk — HMRC PAYE, NI, student loan, and pension thresholds for 2026/27
- 2.Pensions Act 2008 — legislation.gov.uk — Statutory basis for auto-enrolment qualifying earnings
- 3.PAYE reference numbers — HMRC employer guide — Employer reference format used to validate payslip authenticity
- 4.National Insurance rates and categories — gov.uk — NI category letters and the rules that determine which letter applies
- 5.CIFAS Fraudscape annual report — UK fraud trends including application-fraud markers
- 6.FCA Financial Crime Guide — Lender obligations on detecting and reporting application fraud
Editorial process: how we source and review UK tax content.