Obviously, if there is no agreement between the UK and the EU on 29 Mar 2019 then a no deal Brexit will occur.

It is my understanding that any agreement (or article 50 withdrawal) that is negotiated will need approval by both the EU states and the European Parliament. If this is correct how long will this process take and therefore what is the last possible date that a deal can be made?

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    Not sure in general, but note that both sides could agree to an extension so even 29 Mar is a questionable drop dead date.
    – Eremi
    Jun 26, 2018 at 17:10
  • I believe the UK leaving on 29 Mar is now UK law (or will be after Royal assent), so this would need to be changed which could also take a while. Jun 26, 2018 at 17:41
  • @JeremyFrench while it's politically unlikely, it wouldn't take very long to rush a bill through to change UK law on the date. But that would only allow the UK to ask the rest of the EU for an extension. Under article 50, the other countries must agree to it unanimously.
    – phoog
    Jun 28, 2018 at 6:31
  • @phoog So if everyone agrees that leaving on March 29th is a bad idea, they could have a vote on March 27th in the UK, then the EU calls in everyone for a vote on March 28th.
    – gnasher729
    Jun 30, 2018 at 15:26
  • @gnasher729 I'm not sure about EU processes. It might be possible for unanimous agreement to be established through e-mail or by phone. The timeline you contemplate is obviously improbable, but it is possible in theory.
    – phoog
    Jun 30, 2018 at 19:12

2 Answers 2


There is no fixed date.

The article 50 process allows for 2 years for the parties to make arrangements for leaving. It allows for the parties to agree to extend this period (The UK government has said that it will not ask for any extension). The parties have also agreed on an implementation/transition period, so some aspects of leaving can be deferred until then.

There would need for a certain amount of time for the parties to ratify any agreement that is made, probably several months, depending on how complex the agreement is. But there is no fixed deadline.

I would note that the first round of negotiation committed the United Kingdom to "maintain full alignment with those rules of the Internal Market and the Customs Union which, now or in the future, support North-South cooperation, the all-island economy and the protection of the 1998 Agreement." In the case that no other agreement is reached, the exit must be "soft" at least in this aspect.

  • 1
    I like your answer, but I thought the commitments made in the first round were only applicable if there is a full agreement. I am not sure how there can be a 'soft' agreement if nothing is agreed? Jun 26, 2018 at 17:39
  • @JeremyFrench the commitments in the first round are the fallback if no full agreement is reached. They are binding.
    – Josef
    Jul 11, 2018 at 13:14

There is no inevitable date because Article 50 could always be cancelled or the negotiation extended, with mutual agreement from the EU.

However, assuming that the UK wants to stick to the March 29th 2019 date, an agreement needs to be in place by October 2018. The EU and UK will need the remaining time to agree and ratify the deal, if any. If nothing can be agreed by then, then there won't be sufficient time to agree anything.

Having said that, the UK looks likely to agree to certain measures such as the "backstop" for the Irish Border. The divorce will would likely stand too, because defaulting on it would damage the UK's credit rating. As such the hardest possible Brexit looks unlikely now, but a very hard and damaging one is still possible.

  • Thanks for this, would the October deadline also stand for requesting a cancellation or extension of article 50? Jun 27, 2018 at 8:42
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    Interesting question. Since there is no formal procedure to cancel and it has never been done before it's impossible to say for sure, but I think it's very likely that the EU would be able to agree to it fairly quickly. Probably with some agreement that it isn't triggered again any time soon. As for extension I probably depends if the EU members think that it would result in an eventual deal, or if it is just prolonging the inevitable crash.
    – user
    Jun 27, 2018 at 10:20
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    I don't think anything is required to be in place in October 2018, it's just the realisation "if we don't have things in place in October, then we are in trouble when March comes".
    – gnasher729
    Jun 30, 2018 at 15:28
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    If there is no agreement by October 2018 then I don't think the EU will allow itself to be forced into a quick decision unless that decision is either cancel Brexit or take an existing off-the-shelf deal like staying in the EEA and customs union.
    – user
    Jun 30, 2018 at 16:15
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    What’s special about October? Is the remaining time required to get an agreement approved, so a December agreement couldn’t be? Or is it just a ballpark “this is when things look bad” marker?
    – Bobson
    Aug 16, 2018 at 5:43

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