Is ACAS early conciliation compulsory?

Yes for most employment tribunal claims. Section 18A of the Employment Tribunals Act 1996 makes it mandatory to notify ACAS before filing an ET1. There are narrow exceptions (multiple claimants where another has already notified, interim relief, certain national security cases), but for individual claims by employees and workers, the notification step cannot be skipped. The tribunal will reject an ET1 that does not have an early conciliation number.

How long does conciliation last?

Up to six weeks from the day ACAS receives your notification (Day A). The conciliation period ends when either ACAS issues the early conciliation certificate (Day B), or the six weeks expire, or both sides agree to extend by up to two weeks. Many cases resolve in two to three weeks; some are closed within days when one side refuses to engage.

Does the tribunal deadline stop during ACAS conciliation?

Yes. Section 207B of the Employment Rights Act 1996 stops the clock from Day A to Day B. The time that passes between those two days is not counted toward the three-month tribunal deadline. There is also a protective rule that gives every claimant at least one month after Day B to present the claim, even if that pushes the deadline past the original three-month point.

What happens if ACAS conciliation fails?

ACAS issues an early conciliation certificate, which contains a unique reference number. The claimant then has a fixed window to present the ET1 to the tribunal. The certificate is the gateway to the tribunal claim and the tribunal will not accept an ET1 without it. Failure to settle is normal; conciliation succeeds in roughly 30 to 40% of cases.

ACAS Early Conciliation UK (2026): A Plain English Guide

What ACAS does

ACAS (the Advisory, Conciliation and Arbitration Service) is the statutory body responsible for conciliating workplace disputes. It is funded by government, independent of any employer or union, and operates under the Trade Union and Labour Relations (Consolidation) Act 1992. Its role in early conciliation is to attempt to broker a settlement before either side incurs the cost and time of a tribunal hearing.

ACAS officers are conciliators, not advisers. They do not represent either side, do not give legal advice and do not impose decisions. Their job is to carry messages, test the room for movement, and help both sides reach an agreement they could not have reached directly.

ACAS also runs a free helpline, publishes the statutory ACAS Code of Practice on disciplinary and grievance procedures, and conducts post-claim conciliation if the tribunal claim is lodged without a settlement.

When early conciliation is mandatory

Section 18A of the Employment Tribunals Act 1996 makes early conciliation compulsory before bringing most tribunal claims. The rule covers unfair dismissal, constructive dismissal, discrimination, unlawful deduction of wages, holiday pay, redundancy pay, and breach of contract on termination.

Narrow exceptions apply: multiple-claimant cases where another claimant has already notified ACAS for the same dispute, applications for interim relief, certain national security cases, and (in limited circumstances) claims where the respondent has already contacted ACAS. For an individual employee or worker pursuing a typical claim, the notification is mandatory.

Failing to notify means the tribunal will reject the ET1. The notification can be made online at the ACAS website or by phone. A notification takes minutes and is free.

The process step by step

Conciliation runs through a fixed sequence:

Day A — notification. The claimant submits the EC form. ACAS acknowledges receipt and allocates the case to a conciliator. Day A starts the time-limit pause.
First contact. The conciliator calls or emails the claimant to confirm the issues and the desired outcome.
Respondent contact. The conciliator approaches the employer to ask whether they want to engage. The employer can refuse, in which case conciliation ends quickly.
Exploring settlement. The conciliator carries messages between the two sides about the issues, the strength of the case, the figure each is willing to pay or accept, and the non-monetary terms (reference, apology, confidentiality).
Outcome. Either both sides agree terms (recorded on a COT3 form, which is binding); or one side ends conciliation; or the six-week window expires. ACAS issues an early conciliation certificate (Day B). The clock resumes.

The conciliator never asks the claimant to settle for less than they think the case is worth, and never tells the employer they have to pay. Conciliation works through interest exploration, not pressure.

Outcomes

Three outcomes are possible.

Settlement on a COT3. If both sides agree terms, ACAS records the agreement on a COT3 form. The COT3 is a legally binding settlement contract. Once signed, the claimant cannot bring the same claim at tribunal. Many COT3 settlements include a payment, a reference, and a confidentiality clause.

No settlement, certificate issued. If one or both sides refuse, or the six-week window expires without agreement, ACAS issues an early conciliation certificate. The certificate contains a unique number that the claimant uses on the ET1 form. The tribunal deadline window then runs.

Withdrawal or non-engagement. Either side can withdraw at any point. The respondent can refuse to engage from the outset. ACAS will then issue the certificate without further attempts.

Settlement options

Settlements through ACAS conciliation usually combine a financial payment with non-monetary terms. The financial side typically includes a sum for compensation, sometimes structured to maximise the £30,000 tax-free allowance under the Income Tax (Earnings and Pensions) Act 2003. The notice pay and holiday pay components are paid separately through PAYE.

Non-monetary terms commonly include an agreed reference (often a wording-locked “in-form” reference), confidentiality on both sides, a non-derogation clause, and sometimes a payment toward the employee’s legal fees.

A settlement reached through ACAS conciliation is recorded on a COT3 rather than a settlement agreement. The two are similar in effect but the COT3 does not require the employee to take independent legal advice (settlement agreements do, under section 203 of the Employment Rights Act 1996). For complex deals or large sums, claimants often prefer a settlement agreement signed off by a solicitor.

To model the financial side of an ACAS settlement, the settlement agreement calculator produces the gross value from headline inputs. The redundancy pay calculator gives the statutory floor. The can I afford to quit calculator tells you whether the settlement plus other resources will see you through.

Time limits — the stop-the-clock rule

Section 207B of the Employment Rights Act 1996 sets out how ACAS conciliation interacts with the tribunal deadlines. Two protective rules apply.

First, the time between Day A (notification) and Day B (certificate) does not count toward the three-month deadline. If you notify on day 70 of the three-month period, and conciliation lasts 30 days, the deadline is pushed back by 30 days from where it would otherwise have fallen.

Second, the claimant always has at least one month after Day B to file the ET1, even if the original three-month deadline would have fallen earlier. This gives claimants who notify late in the period a buffer.

The interaction between the two rules catches people out. The safe approach is to notify ACAS as soon as you decide to pursue a claim, lodge the ET1 promptly after the certificate, and never assume the tribunal will extend a missed deadline. The detail with worked examples is at the constructive dismissal time limits page (the same rules apply to every claim type).

Risks and limitations

ACAS conciliation is not a forum for fact-finding or legal argument. The officer will not tell you whether your case is strong, will not pressure the employer to pay more, and will not make findings. If both sides have unrealistic positions, conciliation will end without settlement.

The conciliator is also bound by confidentiality. What you say during conciliation cannot later be used as evidence at tribunal. This is helpful because it allows frank conversations, but it also means a strong oral admission by the employer in conciliation cannot be relied on later.

For complex or high-value cases, taking advice before and during conciliation is strongly recommended. A specialist solicitor will know the ballpark settlement figures for your type of claim and can help frame the position.

Useful calculators

Frequently asked questions

Is ACAS early conciliation compulsory?: Yes for most employment tribunal claims. Section 18A of the Employment Tribunals Act 1996 makes it mandatory to notify ACAS before filing an ET1. There are narrow exceptions (multiple claimants where another has already notified, interim relief, certain national security cases), but for individual claims by employees and workers, the notification step cannot be skipped. The tribunal will reject an ET1 that does not have an early conciliation number.
How long does conciliation last?: Up to six weeks from the day ACAS receives your notification (Day A). The conciliation period ends when either ACAS issues the early conciliation certificate (Day B), or the six weeks expire, or both sides agree to extend by up to two weeks. Many cases resolve in two to three weeks; some are closed within days when one side refuses to engage.
Does the tribunal deadline stop during ACAS conciliation?: Yes. Section 207B of the Employment Rights Act 1996 stops the clock from Day A to Day B. The time that passes between those two days is not counted toward the three-month tribunal deadline. There is also a protective rule that gives every claimant at least one month after Day B to present the claim, even if that pushes the deadline past the original three-month point.
What happens if ACAS conciliation fails?: ACAS issues an early conciliation certificate, which contains a unique reference number. The claimant then has a fixed window to present the ET1 to the tribunal. The certificate is the gateway to the tribunal claim and the tribunal will not accept an ET1 without it. Failure to settle is normal; conciliation succeeds in roughly 30 to 40% of cases.

General information about ACAS conciliation, not legal advice. For your specific situation, contact ACAS directly or take advice from an employment-law solicitor.