The Conservative party has contacted all its MEPs to ask them to consider running for election in May if the prime minister’s Brexit deal is defeated on Tuesday.

Ashley Fox, the party’s leader in the European parliament, contacted MEPs to ask them to think about their options in the event that Theresa May’s deal fails again.

“May I ask you to reflect over the weekend whether you would wish to stand as a Conservative candidate. I will speak with you all individually after the MV3 [meaningful vote 3) next week,” he said in a WhatsApp message to MEPs after MPs voted overwhelmingly to delay Brexit on Thursday night.

He said he hoped May would get the deal approved but the party needed to be prepared to field candidates for the European elections, due to be held between 23 and 26 May.

“We need to be ready, if necessary, to take part in the European elections in May and Conservative MEPs are preparing to discuss the next steps,” he said.

The question of whether European elections would be necessary in the event of a Brexit delay is a hotly contested topic, with some saying Britain could simply ignore the elections and others that the UK could have a catch-up vote when the future was clearer.

One prominent Labour MEP said the warning by May and European leaders that the UK would have to hold elections for something so central to Eurosceptics’ hostility towards the EU was as fictional as Frankenstein.

Jean-Claude Juncker, the European commission president, has written to Donald Tusk, the European council president, saying the UK would be legally required to hold the elections if Britain was still in the EU at the end of May.

Claude Moraes, the Labour MEP for London, said: “He sent this letter without any legal advice backing it up. I think this is just a device to create a false discussion about whether MEPs will have to come back or not to force the ERG to vote for May’s deal.

“They know that Brexiters, Eurosceptics and Tories think the European parliament is just a gravy train, waste of money and every time they suggest a long extension period of 21 months, they know it is pressing on that raw nerve.

“It’s like a bolt of electricity to Frankenstein. Nobody expects the corpse to be brought back to life, but somehow Tusk and Juncker create that idea that the elections will have to be held. Most MEPs realise the chances of very, very low of elections.”

Catherine Bearder, the only Liberal Democrat MEP, believes the UK has time to decide whether to have elections and did not necessarily have to have them in May, but could delay to the middle of June when the success or failure of an article 50 extension was clear.

The European parliament confirmed this was technically possible but would require ratification by a qualified majority of the council of ministers.

Richard Corbett, the Labour MEP for Yorkshire and the Humber, said a catch-up election would be a tall order because every parliament would have to vote on it and countries such as Spain, which are holding general elections at the end of April, may not be interested in facilitating such a move.

Bearder, 70, had planned to retire in July but said she was willing to stand again if necessary as it would help her pursue her interests in fighting environmental crimes and human trafficking.

Nigel Farage is already gearing up to field candidates for his new Brexit party, saying elections are “pretty much unavoidable”. He told the BBC earlier this week that he would try his hardest to persuade a European leader to veto any extension to article 50.

Jean Lambert, a Green party MEP for the London region, said her party was continuing to selectcandidates in case of a lengthy Brexit delay, but she thought there was little chance the EU would grant “multiple short extensions” so it was an academic discussion.

If the article 50 extension was lengthy, it would be possible to have “dual mandate” representatives, raising the prospect of MPs also standing as MEPs. This is something that would be anathema to many in Brussels.

Corbett believes there could be plenty of legal challenges from voters if the British decided not to hold elections in the event of a lengthy extension. He revealed that the European parliament’s legal services department had advised MEPs that suggestions the parliament would be rendered invalid if the UK was not represented were incorrect.