EU leaders are watching on in horror at the Tory “catfight” unfolding in Westminster – but will still not make the concessions Theresa May needs to unite the Conservatives when she arrives in Brussels on Thursday.

The prime minister will have a rare two-way discussion with her EU counterparts at the European Council summit on Thursday afternoon, fresh off the plane from surviving a bruising confidence vote in Westminster.

But despite a generally positive tone in Brussels, with officials and diplomats alike suggesting they want to help the prime minister, serious changes to the agreement that would actually win around her MPs will remain effectively off the table.

The prime minister is hoping national leaders will give her breathing space and something to take back to the UK that will ease the ire in Westminster – with a late night meeting to draw up “reassurances” planned.

But EU officials sought to manage expectations ahead of the meeting, with one warning: “What is impossible is to renegotiate the deal from the 25 November. That’s impossible. The rest can be discussed.”

They added: “Renegotiation of the deal that was reached is not on the table and whatever assurances are given cannot contradict the deal that was made on 25 November.”

Brussels essentially gave its backing to the prime minister ahead of the no confidence vote, with a spokesperson for the European Commission stating that Ms May had done a good job of “managing a very difficult process”.

But Guy Verhofstadt, the European parliament’s outspoken Brexit coordinator, voiced the behind-the-scenes exasperation of many in the EU capital.

“Once again, the fate of EU-UK relations, the prosperity of businesses and citizens’ rights are consumed by an internal Conservative party catfight over Europe,” he said.

“I hope that, whatever happens, at least the vote will make clear that a disastrous no-deal is off the table.”

The leaders of the European parliament’s political groups were the latest force to line up behind the EU’s united line of “no renegotiation” on Wednesday as they warned they would use their veto to block any withdrawal agreement that watered down the controversial “backstop”.

The shape and scope of the “reassurances” EU leaders will cook up still looks uncertain. Ahead of the meeting, EU diplomats said they would be decided on the day and would depend on what Ms May asked them for.

One senior official said there was “a wide range of legal forms to offer assurances or clarification”, and did not rule out the possibility of pseudo-legal “protocols” tacked into the treaty. Such protocols would be lodged at the UN with the withdrawal agreement and would provide legal reference – but not change the agreement.

All EU diplomats who spoke to The Independent were adamant that they could not contradict the agreement.

One said: “We believe that when it comes to the backstop, the text of the withdrawal agreement and the text of the political declaration are clear. It is clear and it will be legally binding. If there is something unclear then we need to listen to the prime minister about what is unclear.”

What is the Irish border Brexit backstop?

Unless leaders pull a rabbit out of a hat, signals out of Brussels and other EU capitals so far suggest they will not meet the demands of the Brexiteers – who want the backstop either removed entirely, given a time-limit, or some kind of new exit clause not dependent on EU consent.

Brexit will be far from the only issue discussed at the meeting, which will also begin the heavy-lifting of hashing out the EU’s multi-year budget. The prime minister will share her concerns with leaders in the afternoon, and they will, unusually, be allowed to ask her questions and respond.

The EU has so far tried to keep direct discussion between leaders about Brexit to a minimum – preferring instead that all negotiations go through its adept chief negotiator Michel Barnier and his team.

After a meeting on foreign policy over dinner, which Ms May will attend, the prime minister will leave the 27 leaders to discuss her concerns without her. They are expected to issue a late-night written statement spelling out the steps they are prepared to make to ease the passage of the deal through parliament.

"Brexit betrayal" march in London Show all 43 1 /43 "Brexit betrayal" march in London "Brexit betrayal" march in London A protester holds an anti-BBC sign Angela Christofilou/The Independent "Brexit betrayal" march in London A pro-brexit demonstrator holds a sign in the picket line Angela Christofilou/The Independent "Brexit betrayal" march in London A protester carrying a noose at the "Brexit betrayal" march. The man carrying it told a reporter: "That's what the traitor May deserves." AP "Brexit betrayal" march in London Pro-brexit supporters hold a sign opposed to Nigel Farage Angela Christofilou/The Independent "Brexit betrayal" march in London Protesters carry a defaced British flag on the march Angela Christofilou/The Independent "Brexit betrayal" march in London Tommy Robinson addresses a rally after taking part in a Brexit 'betrayal' march in central London PA "Brexit betrayal" march in London Police officers attempts to keep rival protesters from clashing at the Brexit 'betrayal' march in London Victoria Jones/PA "Brexit betrayal" march in London A protester holds an anti-Theresa May sign Angela Christofilou/The Independent "Brexit betrayal" march in London A pro-brexit demonstrator and his dog Angela Christofilou/The Independent "Brexit betrayal" march in London A pro-brexit demonstrator at the protest Angela Christofilou/The Independent "Brexit betrayal" march in London A pro-brexit sign at the rally Angela Christofilou/The Independent "Brexit betrayal" march in London Pro-brexit demonstrators endorse UKIP Angela Christofilou/The Independent "Brexit betrayal" march in London A Brexit 'betrayal' march protester wearing a Make Britain Great Again hat in London on 9 December 2018 Chris J Ratcliffe/Getty "Brexit betrayal" march in London Brexit 'betrayal' marchers gathering on Park Lane ahead of a protest Angela Christofilou/ The Independent "Brexit betrayal" march in London The "Brexit Betrayal" march passes through Central London Angela Christofilou/The Independent "Brexit betrayal" march in London Tommy Robinson tells protesters to join Ukip via their mobile phones on stage next to leader Gerard Batten (right) at the Brexit 'betrayal' march Gareth Fuller/PA "Brexit betrayal" march in London A protester speaks thorugh a megaphone on the march Angela Christofilou/The Independent "Brexit betrayal" march in London A pro-brexit demonstrator walks in the picket line Angela Christofilou/The Independent "Brexit betrayal" march in London A pro-brexit anti-May sign at the rally Angela Christofilou/The Independent "Brexit betrayal" march in London A protester carries a Union Jack on the march Angela Christofilou/The Independent "Brexit betrayal" march in London A pro-brexit demonstrator wrapped in the Union Jack Angela Christofilou/The Independent "Brexit betrayal" march in London A pro-brexit anti-May sign at the rally Angela Christofilou/The Independent "Brexit betrayal" march in London Pro brexit demonstrators move through Central London Angela Christofilou/The Independent "Brexit betrayal" march in London A pro-brexit demonstrator marches with sign Angela Christofilou/The Independent "Brexit betrayal" march in London A pro-brexit demonstrator holds a rude sign in the rally Angela Christofilou/The Independent "Brexit betrayal" march in London The march passes down Victoria Street near Parliament Angela Christofilou/The Independent "Brexit betrayal" march in London A festive protester marches near Parliament Angela Christofilou/The Independent "Brexit betrayal" march in London A protester holds a mock noose as the march passes down Victoria Street towards Parliament Angela Christofilou/The Independent "Brexit betrayal" march in London A protester wrapped in the Union Jack marches down Victoria Street towards Parliament Angela Christofilou/The Independent "Brexit betrayal" march in London A protester makes some noise on the march Angela Christofilou/The Independent "Brexit betrayal" march in London A protester dressed as a dinosaur holds a sign rallying against "Davocracy" - in reference to the annual World Economic Forum meeting in Davos Angela Christofilou/The Independent "Brexit betrayal" march in London A protester holds a pro-brexit sign on the march Angela Christofilou/The Independent "Brexit betrayal" march in London The march approaches parliament Angela Christofilou/The Independent "Brexit betrayal" march in London A protester distributes pro-brexit lapel badges Angela Christofilou/The Independent "Brexit betrayal" march in London A demonstrator wears an anti-EU poster and holds an anti-BBC sign Angela Christofilou/The Independent "Brexit betrayal" march in London A smoke bomb is deployed in Parliament Square as the march comes across the counter-demonstration Angela Christofilou/The Independent "Brexit betrayal" march in London Angela Christofilou/The Independent "Brexit betrayal" march in London A flag bearing the Arms of Plantagenet flies in theprot Angela Christofilou/The Independent "Brexit betrayal" march in London Protesters on the Brexit 'betrayal' march in London on 9 December 2018 Angela Christofilou/ The Independent "Brexit betrayal" march in London Protesters on the Brexit 'betrayal' march in London on 9 December 2018 Angela Christofilou/ The Independent "Brexit betrayal" march in London Brexit 'betrayal' marchers gathering on Park Lane ahead of a protest on 9 December 2018 Angela Christofilou/ The Independent "Brexit betrayal" march in London Brexit 'betrayal' marchers gathering on Park Lane ahead of a protest on 9 December 2018 Angela Christofilou/ The Independent "Brexit betrayal" march in London Angela Christofilou/The Independent

The European parliament’s conference of presidents, which represents the leaders of its political groups, said in a statement issued on Wednesday afternoon that “the withdrawal agreement and political declaration are fair and balanced and represent, given EU principles, current UK red lines, and the commitments set out in the Good Friday Agreement, the only deal possible to secure an orderly withdrawal from the European Union”.

The group chiefs also “stressed that renegotiating the backstop was not possible” and that without it “parliament would not give its consent to the withdrawal agreement”.

Speaking at lunchtime, Margaritis Schinas, the European Commission’s chief spokesperson, told reporters: “The Commission will not comment on the internal politics of the United Kingdom and not least the Conservative Party, but President Juncker has on many occasions expressed his support for Prime Minister May and her role in managing a very difficult process.”