Mr Barnier’s comments put the Prime Minister on notice that she faces a difficult task when she arrives in Brussels tomorrow to request EU leaders agree a short extension if she can get her deal through Parliament in the next nine days – or a long delay of anywhere from nine to 21 months if not.
“It is our duty to ask whether this extension would be useful because an extension will be something which would extend uncertainty and uncertainty costs,” he said.
Mr Barnier added that a lengthy extension would need to be linked to “a new event or a new political process” to be justified.
He poured cold water on reports that Mrs May could effectively be granted two options for extension – a long delay, with a break clause in May or June if the deal is passed.
“You said both short and long,” he said in response to a question. “Well, it’s either one or the other, isn’t it?”
EU leaders are likely to make their own demands in exchange for a delay, which could include the UK withdrawing from the budget-setting process.
Ministers in EU capitals also used harsh language about the prospect of a long delay, with the French Europe minister Nathalie Loiseau telling reporters in Brussels: “Grant an extension – what for? Time is not a solution, it’s a method – if there is an objective and a strategy and it has to come from London.”
Germany’s Europe minister Michael Roth said the EU was “really exhausted by these negotiations”.
“I expect clear and precise proposals from the UK Government on why an extension is necessary,” he said. “It’s not just a game. It’s an extremely serious situation not just for people in the UK, but also for the people in the EU.”
Downing Street admitted the UK was in crisis after the Commons Speaker blocked a third vote on Mrs May’s Brexit deal unless there was a significant change in circumstances.
The Prime Minister’s official spokesman told journalists that Mrs May had warned MPs ahead of the second vote on her deal that the UK would be plunged into crisis if they failed to back it, adding: “That has come to pass”.
Downing Street confirmed a letter would be sent to the EU Council president Donald Tusk by the end of today, setting out the UK’s request for an extension.
Reports suggested the Prime Minister set out both options for delay at yesterday’s Cabinet meeting without stating a preference, although this was denied by a Government source.
Mrs May’s spokesman said she voiced her “absolute determination” that MPs should have another chance to vote on her Brexit deal, despite the bombshell intervention of Speaker John Bercow.
But Ms Leadsom is reported to have told her colleagues that “this is now a Remain Cabinet, not a Brexit Cabinet”, while the Chief Secretary to the Treasury Liz Truss warned that failure to leave the EU would open the door to a Jeremy Corbyn government.
The Prime Minister’s official spokesman said: “What you can see from the Prime Minister and her colleagues is an absolute determination to find a way in which Parliament could vote for the UK to leave the European Union with a deal.
“The Prime Minister has been very clear throughout that she wants that to happen as soon as possible.”
The spokesman added: “She has said in the House of Commons that she does not want there to be a long delay and that she believes asking the British public to take part in European elections three years after they voted to leave the EU would represent a failure by politicians.”
Earlier, Brexit secretary Stephen Barclay signalled that ministers would press on with Mrs May’s Brexit deal despite the Commons Speaker’s bombshell intervention.
Mr Barclay said that, while the Cabinet would give “serious consideration” to his ruling, Mrs May’s plan remained “the only deal on the table”.
“What we need to do is secure the deal,” he told Sky News. “This is the only deal on the table. The EU is clear it is the only deal on the table. Business need the certainty of this deal and it is time that Parliament comes together and gets behind it.”
Mr Barclay acknowledged the ruling made it “more unlikely” that there would be an attempt to get the deal through the Commons before Mrs May attends the EU summit in Brussels tomorrow.