last updated at 2.21pm -
Britain has asked EU leaders to delay Brexit until June 30, Prime Minister Theresa May told parliament on Wednesday, on the eve of an EU summit in Brussels.
May said she had written to EU President Donald Tusk "informing him that the UK seeks an extension to the Article 50 period to June 30".
But according to a European Commission internal briefing note ahead of an EU summit this week, delaying Brexit to June 30 would bring "serious legal and political risks".
Elections to the European Parliament will be held on May 23-26, and the commission said that if Britain is granted a long delay, it must organise ballots.
"Any extension offered to the United Kingdom should either last until 23 May 2019 or should be significantly longer and require European elections.
"This is the only way of protecting the functioning of the EU institutions and their ability to take decisions," said the commission note, which was prepared on Wednesday morning before May's letter was received.
It will be for the leaders to decide on the length of the extension -- and all 27 must give their approval -- but the commission said they faced a "binary" choice: May 23 or the end of 2019 at the earliest.
"Any other option (as for example an extension until 30 June 2019) would entail serious legal and political risks for the European Union and would import some of the current uncertainties in the United Kingdom into the EU27," it warned.
If a long extension is granted, Britain must commit to "constructive abstention" in key EU debates such as the bloc's budget and appointments to the next commission, due to be constituted later this year.
This is to stop Britain using its veto to block EU business as a tactic to secure more Brexit concessions from Brussels.
In a similar vein, the commission said it must be made clear that if an extension is granted, it cannot be used to renegotiate the withdrawal agreement struck between the EU and Britain.
Exasperated European leaders are demanding London tell them clearly what it wants, warning that the risk still remains that Britain could crash out of the bloc, ending its 46-year membership without formal arrangements.
The British premier is struggling to keep control of the Brexit process after MPs last week decisively rejected the EU divorce deal for a second time.
She has reluctantly accepted that Brexit must be postponed, amid fears of an economic shock if Britain ends its membership of the EU with no new arrangements in place.