Theresa May is facing an explosive backlash from all ranks of her party over the UK’s participation in next month’s European elections, as another Brexit delay looks all but inevitable.

Conservative HQs confirmed the fears of many members, MPs and ministers when it asked activists to apply to be candidates as the party “will be contesting the European elections on 23rd May”.

The Government also laid the Day of Poll order in parliament “as part of lawful and responsible contingency operations” for the election, admitting it would “damage trust in politics”.

The Prime Minister previously said it would be unacceptable for the UK to take part in the Brussels poll almost three years after the Leave vote.

Brexiter Tory MPs, who loathe participating in the election and warn the Conservatives will be routed by Nigel Farage’s new Brexit party, are now trying to hold a confidence vote in the PM.

Although Mrs May cannot be formally challenged until December because she recently saw off a no confidence vote, the 1922 committee of Tory backbenchers was last night being urged to hold an ‘indicate vote’ instead.

There was little sign of an eleventh-hour compromise between Labour and the Government which could break the impasse over Brexit at Westminster.

Jeremy Corbyn spoke of his party’s “frustration” that Mrs May had not moved away from her red lines and towards a compromise on a permanent customs union.

He said: “The priority is to prevent crashing out with no-deal. We’re prepared to talk and put forward our views, but talks have to mean a movement, and so far there’s been no change in those red lines.”

The executive of the 1922 committee also warned Mrs May in Downing Street against agreeing to any customs union with tariffs be set by the EU., which could inhibit other UK trade deals.

Although government and opposition officials had “technical” discussions on Monday, substantial talks between ministers and Labour’s frontbench will not restart until today.

The Prime Minister will also be out of the country for much of today, pleading the case for a short Brexit delay, making an eleventh-hour deal at home with Mr Corbyn even more improbable.

Mrs May will meet German Chancellor Angela Merkel in Berlin and then French President Emmanuel Macron in Paris ahead of a crunch EU summit in Brussels tomorrow.

The Prime Minister will ask Europe’s key power brokers to support her request to extend the Article 50 withdrawal process beyond the current no-deal deadline of 11pm on Friday.

Mrs May wrote to EU council president Donald Tusk last week asking for an extension until June 30, offering to start work on the EU elections as a contingency measure, but also reserving the right to scrap them if a Brexit deal was struck with Labour or an agreement reached in the Commons through binding votes on different Brexit options.

However Mr Tusk said he wanted a one-year ‘flextension’ until spring 2020, with a break clause allowing an earlier UK departure if a withdrawal deal was ratified in Westminster.

A meeting of EU foreign ministers in Luxembourg yesterday suggested there was a willingness to grant a delay, but also a determination to set conditions.

These could include a promise not to play hardball - perhaps under a new Brexiter PM - in next year’s long-term budget setting process, and in the choice of the next EU Commission.

Arch Brexiter Jacob Rees-Mogg has advocated the UK disrupting the European project from within if a long extension means it remains in the EU beyond June 30.

There is also deep concern among Labour MPs that any deal agreed with Mrs May on a customs union could be ripped up her successor.

The other 27 EU nations must agree unanimously on any extension.

In a letter to MPs, the Cabinet office minister David Lidington and Attorney General Geoffrey Cox explained why they had been forced to commence the legislation for the EU poll.

“It should be clear to all Members of Parliament that asking the public to take part in elections for an organisation that they voted to leave three years ago would damage trust in politics,” they wrote.

“To comply with both EU and domestic law the Government is required to act now in order to make preparations for holding elections - to fail to do so would be to make it impossible to hold elections even if we had not left the EU.

“We reiterate that the order does not make the elections inevitable. If the UK ratifies the deal to leave the EU before the date of election that will automatically remove our obligation to take part and we would cancel them.”

EU chief Brexit negotiator Michel Barnier met Taoiseach Leo Varadkar in Dublin, and said the EU would be happy to offer the UK a customs union.

He also said the EU would stand “fully behind Ireland”, and warned that commitment could mean locking the UK out of EU trade talks for years, forcing it deal with the bloc on WTO terms.

He said: “I have said before, the backstop is currently the only solution we have found to maintain the status quo on the island of Ireland.

“If the UK were to leave the EU without a deal, let me be very, very clear. We would not discuss anything with the UK until there is an agreement for Ireland and Northern Ireland, as well as for citizens’ rights and the financial settlement.”

In the Lords, peers passed the fast-tracked EU Withdrawal Bill created by Tory Oliver Letwin and Labour’s Yvette Cooper to prevent a no-deal Brexit, and it returned to the Commons.

On Monday night, MPs approved the Bill, accepting the final Lords amendment by 390 votes to 81 – a majority of 309.

Commons Leader Andrea Leadsom said if MPs agreed to it following Lords amendments - allowing it receive Royal Assent and become law - the Government was expected to bring forward a motion to extend the Brexit process until June 30 today. She called the Bill “a huge dog’s dinner”.

SNP MP Patricia Gibson said MPs had “wrested control” because of Government “mismanagement”.

Referring to talks with Labour, a Downing Street spokesman said: “We are committed to finding a way through in order to ensure we can leave the EU and deliver on the referendum.

“That will require the parties to work at pace in order to address outstanding issues – and so Ministers and their shadow counterparts will be holding talks tomorrow [Tuesday].”

A spokesperson for the Scottish Greens said:  “I’m delighted that the Tories appear to have finally accepted that the EU elections will take place. The Scottish Greens already have a strong and diverse field of candidates that our members will pick from over the next couple of weeks. The people of Scotland will have the opportunity to let this Government and the toxic Brexiteers that have plunged the country into chaos know what we think.”