Through seven mechanical tests run on every payslip submitted, each targeting what a real payroll system leaves behind that a fabricated document cannot reproduce. 2025/26 figures below come from HMRC's rates and thresholds for employers.
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 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, 2025/26 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 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 and the FCA Financial Crime Guide. 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
- Rates and thresholds for employers 2025 to 2026 — gov.uk — HMRC PAYE, NI, student loan, and pension thresholds for 2025/26
- Pensions Act 2008 — legislation.gov.uk — Statutory basis for auto-enrolment qualifying earnings
- PAYE reference numbers — HMRC employer guide — Employer reference format used to validate payslip authenticity
- National Insurance rates and categories — gov.uk — NI category letters and the rules that determine which letter applies
- CIFAS Fraudscape annual report — UK fraud trends including application-fraud markers
- FCA Financial Crime Guide — Lender obligations on detecting and reporting application fraud
Editorial process: how we source and review UK tax content.