My payslip has BR, D0, K, M1 or a strange code
Decode the code first, then check whether it is temporary, split across jobs, or recovering an underpayment.
Pick the HMRC problem
I received a P800, P2, SA250, SA316 or penalty notice
Identify the document type before you pay, appeal, ignore or call HMRC.
I think I was put on emergency tax
Estimate the likely refund route and whether the issue is payroll timing or a code correction.
I am not sure whether I need Self Assessment
Use the readiness checklist before waiting for a letter or missing a deadline.
I need to know what is due and when
Use the calendar for January filing, payments on account, year-end and April reset dates.
My income changed and the tax feels wrong
Run the income baseline after decoding the letter or code so the numbers make sense.
HMRC how-to deep dives
Ten step-by-step procedural guides for the most common HMRC interactions. Use these when you need to actually do something — write a letter, file a claim, dispute a decision, set up a payment plan.
Template letters for tax code, refund and appeal
Four free template letters with the right postal addresses and what to include in each.
How to check your tax code online
Step-by-step walkthrough of the Personal Tax Account and HMRC app for 2026/27.
How to register for Self Assessment
SA1 vs CWF1 vs SA401 forms, UTR timeline, activation code, deadlines and penalties.
SA walkthrough — every box explained
Page-by-page guide to SA100 + supplementary pages (SA102/103/105/106/108) with the Payments on Account trap.
Higher-rate pension relief — the missing 20-25%
How to claim what most higher-rate taxpayers miss. Three routes; backdate four years.
Marriage Allowance — retrospective claim
Backdate to 6 April 2022 for up to £1,008, plus up to £252 for 2026/27 (GOV.UK). Death-of-spouse cases included.
How to claim work-from-home tax relief
The employee relief ended on 5 April 2026. How to claim £6 a week for 2022/23 to 2025/26, the evidence HMRC asks for, and what employers can still pay tax-free.
How to dispute a tax bill
Internal review → Statutory Review → First-tier Tribunal. Time limits, costs and when to use a tax adviser.
HMRC wait times + contact channels
Best time to phone, all department numbers, webchat hours, app capabilities and post addresses.
Can't pay? Time to Pay arrangements
Online TTP setup, eligibility, hardship cases, what happens if you ignore the bill.
Do not skip the evidence step
| Before you respond | Why it matters |
|---|---|
| Take a photo or download the document | You need the reference, date, tax year and exact wording if you challenge or compare later. |
| Check the tax year | Many HMRC letters relate to a previous tax year, not the payslip you are looking at now. |
| Compare with payslips, P60 or P45 | The quickest fix is often spotting which employer, pension provider or benefit is driving the code. |
| Save a scenario | Keep the calculation that explains why you think the result is right or wrong. |
Editorial accountability
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How UK Tax Drag holds itself to account
Pages are checked against the primary sources listed on each page and reviewed by the Editor; corrections are logged in the changelog. Pages are drafted with the help of AI tools (how AI is used). No affiliate revenue. No sponsored content. No paid placements.
UK Tax Drag is an independent publication by Finsolve Consulting Limited, not affiliated with or endorsed by HMRC, GOV.UK or any government body.