Europe’s top politicians set the scene for a major clash with the UK as Theresa May prepared to head back to Brussels in what was branded a “crazy” bid to reopen Brexit talks.

They accused British Eurosceptics of playing a “blame game”, attacked the prime minister for wanting to unpick the deal she agreed to herself, and again reiterated that the backstop Ms May wants to change will not be rewritten.

Among politicians who lined up against Ms May were Jean-Claude Juncker, Michel Barnier, Guy Verhofstadt, a key ally of Angela Merkel, Elmar Brok, and a string of European foreign ministers.

Downing Street aides said on Tuesday they had expected a backlash from Brussels in the wake of Ms May’s demand to reopen the withdrawal agreement, but the force of the reaction from the continent on Wednesday makes her strategy look more difficult than ever.

It comes as Ms May held further meetings in the UK with MPs, including Labour leader Jeremy Corbyn, whilst the flimsy Tory truce that held on Tuesday to give her a win in the Commons already began to crumble.

Speaking in the European parliament as news of Ms May’s plan to reopen talks sank in, Mr Brok said: “Now the British want to renegotiate something that they proposed themselves in the first place. I think this is quite crazy.”

The MEP from Ms Merkel’s CDU party, added: “You in London have to sit down and talk to each other and decide what you want.”

European Commission president Mr Juncker said the bloc had repeatedly told the UK there could be no change to the agreement’s controversial backstop policy, saying: “The withdrawal agreement is the best and only deal possible.

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“The European Union said so in November, we said so in December, we said so after the first meaningful vote in the Commons in January.

“The debate and vote in the House of Commons do not change that.”

When I hear some people who were part and parcel of the negotiations saying what they’re saying, it’s tough – I find it hard to accept this blame game that they’re trying to play against us Michel Barnier

It came after Ms May won a majority for a plan to go back to Brussels and renegotiate the withdrawal agreement she spent 19 months sealing, with the intention of removing the Irish backstop.

This comes into play if the EU and UK cannot agree a future trade deal by December 2020, preventing a hard border in Ireland, but also potentially locking the UK into a permanent customs union.

Speaking at the same debate in Brussels, European parliament Brexit coordinator Guy Verhofstadt said Ms May was always welcome in Brussels for discussions, but added: “For what? To do what?”

Mr Barnier said: “For the first time yesterday ... Theresa May openly called to reopen the withdrawal agreement, even before the vote late in the evening.

“She took distance from the agreement she herself had negotiated and on which we have achieved an agreement.”

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He also took an apparent swipe at former Brexit secretaries Dominic Raab and David Davis, criticising MPs “who negotiated with us”.

“When I hear some people who were part and parcel of the negotiations saying what they’re saying, it’s tough – I find it hard to accept this blame game that they’re trying to play against us,” he said.

“We ourselves talked of so-called alternative arrangements which could prevent the return of a hard border. Only, no one, on either side, was able to say what arrangement would be needed to ensure controls on goods, animals and merchandise, without having a border,” Mr Barnier told France’s RTL radio.

“We have neither the time, nor the technologies.”

French president Emmanuel Macron said the withdrawal agreement was “not renegotiable”, while a spokesman for Ms Merkel said that reopening the deal was “not on the agenda”.

Germany’s foreign minister, Heiko Maas, said: “Germany and the entire union are firmly on Ireland’s side. We will not allow Ireland to be isolated on this issue.”

French Europe minister Nathalie Loiseau said: “The withdrawal agreement that is on the table is the best possible agreement. Let us not reopen it.”

Ashley Fox, the leader of the UK Conservative group in the parliament, said that the approach EU politicians were taking was counterproductive.

He said: “The backstop in its current form will not prevent a hard border, it will create it. It’s simply not good enough to repeat ad nauseam that the deal cannot be amended. That leads to no deal and a hard border”.

Downing Street has suggested that the UK could argue for a time limit or exit clause to the backstop or swapping it for a free trade agreement, as proposed in the so-called Malthouse compromise drawn up by MPs from the Tories’ Remain and Leave wings.

The prime minister’s official spokesman said: “The EU had said it was seeking clarity – there had been suggestions that the backstop was not the main issue of concern, which had originated in Brussels.