How long do written warnings stay live?
There is no statutory duration — ACAS guidance suggests 6–12 months for a first written warning and 12 months for a final, with longer periods only for exceptionally serious conduct.
There is no legally prescribed duration for a written warning. The question is governed by ACAS guidance, your disciplinary policy, and the principle of reasonableness.
Typical durations
ACAS guidance and tribunal case law support the following as reasonable in most cases:
- First written warning: 6 to 12 months.
- Final written warning: 12 months.
- Exceptionally serious conduct: up to 24 months may be justified, but this is the upper limit and should be reserved for cases close to gross misconduct.
Anything beyond 24 months is hard to defend as reasonable, except in very specific industries with safety-critical concerns.
What "live" means in practice
While a warning is live:
- If the employee commits further misconduct, the employer can escalate to the next level on the sanctions ladder (first written → final written → dismissal).
- The warning sits on the employee's HR file as a current matter.
- Performance management decisions (promotion, references) may legitimately take it into account.
What happens when a warning expires
- The warning is disregarded for disciplinary purposes.
- It must not be used as a step in a future disciplinary process.
- A repeat of the same conduct after expiry should be treated as a fresh first-stage matter.
- Referring to an expired warning to justify a later sanction will likely render that sanction unfair.
Best practice
- State the duration in the warning letter — be specific ("This warning will remain live for 12 months from the date of this letter").
- Diarise the expiry date in the HR system.
- Hold a brief review meeting at the end of the period to confirm in writing that the warning has expired.
- Confirm expiry in writing to the employee.
- Do not keep warnings live indefinitely — this is the single most common procedural failing in disciplinary case law.
UK GDPR implications
A warning held on file beyond its legitimate purpose may breach the data minimisation principle of UK GDPR. Once a warning has expired and is no longer needed for any legitimate purpose, it should be reviewed for deletion or anonymisation. A clear retention policy helps.
Official source: ACAS — Disciplinary Procedures.
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Read articleThis article is reference content, not legal advice. UK employment law changes frequently; while we verify articles regularly against the named source, you should always check the current position with a qualified employment solicitor for any specific decision. Complyer Editorial Team · Updated May 2026.