UK payroll, explained from the spec

How UK payroll actually works under the hood: RTI, benefits in kind, National Insurance and the HMRC specs that payroll software is built against.

Articles

Amending a CIS return: the spec says don't, the schema can't, and HMRC decides by letter
24 September 2026 ·18 min read
HMRC's software spec says CIS return corrections must not be sent online. Everyone sends them anyway, the schema can't say "replace", and a letter with a 14-day deadline decides the rest.

CIS construction industry scheme CIS300 HMRC
The payrolling benefits spec is out. How my predictions did
24 September 2026 ·5 min read
In August I predicted what HMRC's 2027/28 payrolling spec would look like. It landed on 16 September 2026. Ten predictions scored, plus the one thing I said that was wrong.

benefits in kind payrolling RTI FPS
The pension law that passed in 2023 and still isn't switched on
13 September 2026 ·8 min read
The 2023 Act lowers auto-enrolment to 18 and takes contributions from the first pound. Three years on, not one regulation has been made. What it would do, and why it's stuck.

auto-enrolment pensions qualifying earnings legislation
The BACS hash: HMRC's payment check that sounded good and caught nobody
23 August 2026 ·13 min read
For eleven years payroll software had to send HMRC a SHA-256 hash of every Bacs payment so they could check the money matched. It couldn't tell who was paid, and one email retired it mid-year.

RTI FPS BACS SHA-256
Payrolling benefits from April 2027: predicting the spec HMRC hasn't published yet
14 August 2026 ·13 min read
HMRC's 2027/28 payrolling-of-benefits spec isn't out until autumn 2026, but its shape is predictable. What the FPS will carry, how Class 1A goes real-time, and where software will hurt.

benefits in kind payrolling RTI FPS