After three years of debate and negotiation there is little new under the sun when it comes to Brexit. But it is rumoured in Westminster, and hoped in Brussels, that Boris Johnson is to revert to a Northern Ireland-only backstop as he seeks to move past the Brexit impasse and avoid breaking his word and extending the UK’s membership beyond 31 October.

What is an NI-only backstop?

The British government’s version of Brexit involves the UK leaving the single market and customs union, requiring the return of a range of checks on goods crossing the border between Northern Ireland and the Republic of Ireland. The “backstop” is intended as a placeholder to ensure such checks do not have to be imposed between the end of the stand-still transition period that is offered in the withdrawal agreement and the start of an all-solving future economic relationship.

The backstop in the current withdrawal agreement would temporarily keep Northern Ireland in the single market, meaning some checks on goods entering Northern Ireland from Britain. But the whole of the UK would stay in a shared customs territory with the EU. This insurance arrangement was negotiated by Theresa May because the then prime minister was of the opinion that no British prime minister could countenance agreeing to the EU’s first proposal: a backstop that involved only Northern Ireland staying in the EU’s customs territory. That would involve a customs border being drawn in the Irish Sea. May described it as a threat to the constitutional integrity of the UK.

Why has the NI-only backstop re-emerged as a possible solution?

Boris Johnson has been thwarted from holding a general election or taking the country out of the EU without a deal on 31 October. But the prime minister has also said he would rather “die in a ditch” than ask the EU for an extension to the UK’s membership. Logic would suggest his only option now would be to agree a tweaked deal with the EU and bring it back to parliament in October. He has opened the current talks by proposing an all-Ireland agrifood zone, which is one part of a Northern Ireland-only backstop. The suggestion is that he will seek to quietly build on that with further NI-only arrangements. Johnson’s EU envoy, David Frost, has already sought to discuss governance with the EU of any NI-only arrangements.

Will the EU agree?

Given an NI-only backstop was an EU proposal in the first place, the U-turn would be warmly welcomed although attempts to give the Northern Ireland assembly a veto on its continuation would not be acceptable.

Is it likely to be the solution?

It is difficult to see where Johnson finds a majority in parliament. Labour, the Democratic Unionists and a large number of Conservative backbenchers have opposed the NI-only backstop in the past. An NI-only arrangement does, however, allow the UK to pursue its own trade policy, unlike the backstop in the withdrawal agreement. It could be the landing zone after a general election for a newly returned Johnson administration if the parliamentary arithmetic has changed.