Before submitting an employment tribunal claim, you must notify ACAS and go through early conciliation — a mandatory step under Employment Tribunals Act 1996, section 18A. From 1 December 2025, the maximum early conciliation period doubled to 12 weeks under the Employment Tribunals (Early Conciliation: Exemptions and Rules of Procedure) (Amendment) Regulations 2025. If conciliation fails, ACAS issues a certificate and you then have at least one month from the certificate date to file your claim. The clock on your original time limit is paused throughout. Updated June 2026.
Source: Employment Tribunals Act 1996, s.18A; Employment Tribunals (Early Conciliation: Exemptions and Rules of Procedure) (Amendment) Regulations 2025; acas.org.uk/early-conciliation.
What the law says
Early conciliation became mandatory for most employment tribunal claims from 6 May 2014 under the Employment Tribunals Act 1996, s.18A (inserted by the Enterprise and Regulatory Reform Act 2013). Claimants must contact ACAS before lodging a tribunal claim. The tribunal will reject a claim that does not include a valid ACAS early conciliation certificate number, unless an exemption applies.
From 1 December 2025, the Employment Tribunals (Early Conciliation: Exemptions and Rules of Procedure) (Amendment) Regulations 2025 extended the maximum conciliation period from six weeks to 12 weeks. This change gives more time for parties to explore settlement without proceeding to the cost and stress of a full tribunal hearing.
Source: acas.org.uk/early-conciliation.
Step-by-step: how early conciliation works
Step 1 — Notify ACAS
Contact ACAS to notify them of the dispute. You can do this:
- Online: acas.org.uk/early-conciliation
- By phone: 0300 123 1100
You provide your details, your employer's details, and a brief description of the dispute. You do not need a solicitor at this stage.
Time limit: In most cases, you must notify ACAS within 3 months minus 1 day of the act (or last act) you are complaining about — for example, within 3 months minus 1 day of your dismissal date for an unfair dismissal claim.
Step 2 — ACAS contacts both parties
ACAS will contact both you and your employer separately. They will explain the conciliation process and ask whether both parties are willing to engage. Neither party is obliged to accept conciliation.
Step 3 — Conciliation takes place (up to 12 weeks)
If both parties agree to engage, ACAS assigns a conciliator who acts as a neutral go-between. The conciliator:
- Does not act as judge or decide who is right.
- Helps both parties understand their respective positions.
- Explores whether a negotiated settlement is achievable.
- May discuss what a tribunal would likely award, to help parties assess the value of settlement.
The conciliation period can last up to 12 weeks from 1 December 2025. Either party can end it early by telling ACAS they do not wish to continue.
Step 4 — ACAS issues the conciliation certificate
If conciliation does not result in a settlement — either because it fails, time runs out, or a party opts out — ACAS issues a conciliation certificate. This contains a unique reference number that must be included in any subsequent tribunal claim.
The certificate is not a finding of fault by ACAS. It simply confirms the early conciliation requirement has been met.
Step 5 — Submit the tribunal claim
Once you have the conciliation certificate, you can submit your employment tribunal claim form (ET1) to the tribunal. You must do this within:
- At least one month from the date the conciliation certificate was issued (the one-month minimum guarantee), or
- The remainder of your original time limit — whichever is longer.
Source: Employment Tribunals Act 1996, s.18A; acas.org.uk/early-conciliation/how-early-conciliation-works.
The "stop the clock" rule explained
Early conciliation pauses your tribunal time limit. Here is how it works in practice:
Example: An employee is dismissed on 1 January 2026. The normal time limit for an unfair dismissal claim is 3 months minus 1 day — i.e., by 31 March 2026. The employee notifies ACAS on 20 March 2026 (11 days before the deadline). The clock stops on 20 March 2026. Conciliation runs until 12 June 2026 (12 weeks later). ACAS issues the certificate on 12 June 2026. The employee now has until 12 July 2026 (one month after the certificate) to submit their claim — because the one-month minimum guarantee exceeds what remained of the original time limit.
Missing the original time limit and then failing to notify ACAS will result in the claim being out of time. Tribunals have very limited discretion to extend time for unfair dismissal claims.
Source: acas.org.uk/employment-tribunal-time-limits.
Changes to time limits from October 2026
The Employment Rights Act 2025 will extend most employment tribunal time limits from 3 months to 6 months, expected to take effect from October 2026 (subject to commencement — check GOV.UK). This will significantly change the window for bringing claims. The early conciliation requirement will remain. Source: Employment Rights Act 2025; acas.org.uk/employment-tribunal-time-limits.
COT3: the ACAS settlement agreement
If conciliation is successful and the parties reach an agreement, ACAS records it in a COT3 form. The COT3 is a legally binding settlement of the claim — once signed, the claimant cannot pursue the same issues to tribunal.
Key differences from a settlement agreement (compromise agreement):
- A COT3 does not require independent legal advice from the claimant (unlike a settlement agreement under ERA 1996, s.203).
- A settlement agreement provides broader legal protection for the employer — it can settle claims that have not yet been brought, whereas a COT3 only settles claims that are in the ACAS early conciliation process.
In practice, larger or more complex settlements are often documented as a settlement agreement. Smaller, more straightforward claims are commonly settled by COT3. Source: ERA 1996, s.18; acas.org.uk/settlement-agreements.
When early conciliation is not required
A small number of tribunal claims are exempt from the mandatory early conciliation requirement. These include:
- Claims involving more than one claimant (in certain circumstances).
- Claims where ACAS has already conciliated on the same dispute.
- Claims for interim relief (for example, whistleblowing dismissal cases where speed is essential).
- Claims where the respondent is already in early conciliation on the same dispute under a separate notification.
If in doubt, contact ACAS — starting the notification process always satisfies the requirement and can only help.
Employment tribunal hub
For more on the tribunal process and compensation, see the employment tribunal hub. For unfair dismissal rights and compensation limits, see the unfair dismissal guide. For tribunal award figures, see employment tribunal awards UK.
Frequently asked questions
See the FAQ below. ACAS guidance on early conciliation is at acas.org.uk/early-conciliation. Call the ACAS helpline on 0300 123 1100.
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