The defeat of the withdrawal agreement in the House of Commons has qualitatively changed the rationale for any potential demand by the UK for an extension to article 50.

The idea of a short – ie, about two months – “technical extension” to allow the completion of legislative work ahead of an agreed departure by the UK was never going to be problematic for the remaining EU27.

But that option is now out, and when MPs almost certainly vote on Thursday for an extension they will have to come up with a new convincing rationale – a “reasoned case” for an extension that can promise a definitive result at the end of it, as both Michel Barnier and Donald Tusk have been repeatedly demanding.

“Prolong this negotiation, to do what?” Barnier, the EU chief Brexit negotiator, asked MEPs at the European Parliament’s plenary session in Strasbourg on Wednesday morning. “The negotiation on article 50 is over. We have a treaty. It is here.”

He said the EU “has gone as far as we could” to encourage MPs to back the deal and added that “the UK must tell us what it wants for our future relationship”.

‘Credible justification’

European Council president Donald Tusk said the night before that “the EU27 will expect a credible justification for a possible extension and its duration. The smooth functioning of the EU institutions will need to be ensured.”

Commission spokesmen refuse to be drawn on their preference for the duration of such an extension if adequately justified. But they are more willing than previously to entertain the idea that a long extension is feasible.

One source argued that a short extension, in the context of the Commons deadlock, would now be incapable of resolving the underlying issues. There is no way prime minister Theresa May would have time to negotiate further assurances and build a majority for the withdrawal agreement, or avoid a no-deal departure, which no one wants.

It would be reasonable in that context, the source suggested, for the 27 to consider a long extension involving continued UK membership for up to a year, during which time many things could happen – a general election, a second referendum, or even the construction of a new May majority.

A long extension might, however, have more difficulty attracting a unanimous vote of the 27 and is likely to raise a storm on the Tory backbenches, where it would be seen as a ruse to delay or even reverse Brexit.

It would not be an easy sell for Theresa May.