15/04/2019 06:00 BST | Updated 15/04/2019 09:02 BST

May Avoided No-Deal, But Her Biggest Brexit Challenge Is Yet To Come

Leaving the EU might have been delayed to Halloween, but will this be a trick or treat for the Prime Minister?

Theresa May has met with EU leaders and another new departure date has been agreed. Instead of leaving last Friday, Brexit has been delayed until 31 October – but is this a trick or treat?

The added time is more than what May asked for and allows an opportunity for different options. But whichever happens, May’s biggest challenge to implementing Brexit is yet to come – and her nightmare could well continue after Halloween.

A snap election is now possible. If May could win a majority, this would see her deal passed by the summer. Or we could hold a public vote on whether to back her deal or back out ending Brexit. MPs would be compelled to vote through May’s deal as they were to support triggering Article 50 after the last referendum.

Both options face huge uncertainties. The biggest is that May might be forced out of office and see the plug pulled on Brexit. Such a total rejection of her government’s efforts would do real damage to both her legacy and party which is likely why she refuses to consider either.

However, May’s Brexit Halloween is haunted by a spectre larger than this. Parliament is gridlocked unable to agree terms about our Withdrawal Agreement. This is a problem, but finding a majority does not mean Brexit then happens.

Missing in all the countless discussions about what the Prime Minister needs to do to pass her deal is that this is the easier part of Britain’s Brexit. If the UK is to leave at any point this year, Parliament must also agree an implementation bill – and, if the current impasse over May’s deal is anything to go by, this is far more of an obstacle to Brexit being signed off before November.

The implementation bill is where Parliament must formally approve the £39billion divorce bill which could still rise depending on how long Britain is stuck in a transition period agreeing a new trade agreement still to follow. This figure is likely to come under intense scrutiny by friends and foes of Brexit alike.

Moreover, if we are to have any transition period, Parliament must legislate for the temporary supremacy of EU law during the entirety of this process. This is non-negotiable insofar as we would be bound by EU law during that period. But if Brexit spectators thought debate over the Irish backstop was politically difficult, MPs wanting Brexit voting for the UK to be bound by the ECJ for the whole of a transition that could last for years may be politically toxic. Yet without agreement, we leave without a deal – whether or not Parliament comes to accept May’s withdrawal agreement.

The challenge for the government is if they think times are tough now, they will almost certainly get tougher and before any talks about future trade deals begin. It will be challenging for May to get agreement on withdrawal and implementation by October without a change in circumstances. She might now want to stand down, call an election or consider a public vote. However her plans for Brexit make necessary one of these options happens shortly.

Thom Brooks is Dean of Durham Law School and advised the Electoral Commission on the EU Referendum