THERESA May ignored advice from Jean-Claude Juncker that requesting a Brexit delay beyond the last week of May could be “legally” problematic.

Despite being told by Juncker of the difficulties in asking for an extension to the Article 50 process that went past the European Parliament elections on 24 to 26 May, the Prime Minister did just that writing to EU leaders asking for a postponement until 30 June.

The revelation came on another day of high drama and growing crisis at Westminster over the government’s plans to leave the EU, due in just eight days.

May will today meet the leaders of the 27 remaining EU members in Brussels where there is growing frustration with the UK.

“President Juncker thinks it is good that the PM sets out her thoughts to the leaders ahead of the (EU summit).

However, President Juncker has formally warned the PM against including a date for the extension that is after the EP elections,” a spokeswoman for Juncker said yesterday.

“That’s why he repeated to her his advice ... that the withdrawal has to be complete before 23 May – otherwise we face institutional difficulties and legal uncertainty. European Parliament elections have to be held [in the UK] if the extension date is after 23 May.”

An EU document obtained by the Reuters news agency said leaders meeting May at today’s summit faced a “binary” choice of a short delay of Brexit from March 29 to before May 23 or a long delay to at least the end of this year, with the UK obliged to hold an election on May 23 for European Parliament.

“Any extension offered to the United Kingdom should either last until 23 May 2019 or should be significantly longer and require European elections,” the document said.

“This is the only way of protecting the functioning of the EU institutions and their ability to take decisions.”

The problems relate to the situation that EU nations are due to receive an additional allocation of parliamentary seats after Brexit and need to know by mid- to late April if they will get these or not if Britain takes part in he elections.

The document also said that in any extended membership, the UK should, “in a spirit of loyal cooperation”, commit to “constructive abstention” on key issues, such as the EU’s long-term budget and filling top EU posts after the May election.

Any request for an Article 50 extension must be agreed unanimously by the EU27 and while European Council President Donald Tusk yesterday said “a short” extension may be possible of May’s deal is passed in Parliament, a number of EU nations were raising the prospect that they would veto May’s request.

It was reported by the Press Association news agency last night that France, Spain, Belgium and possibly Italy were ready to veto a Brexit extension without evidence Parliament is now ready to accept a deal and “the deadlock can be broken”.

There is worry among the EU27 there is no point to an extension as, even after 1000 days of negotiation, May’s deal keeps being rejected and the EU cannot move any further towards the UK.

One source said: “We’re not against an extension per se but we need to have two things – first a demonstration that the situation has changed and there is a guarantee the extension is for something and second that an extension won’t be detrimental to the EU.”