Britain has asked EU leaders to delay Brexit until June 30, Prime Minister Theresa May told parliament on Wednesday, on eve of an EU summit in Brussels.

Britain's Prime Minister Theresa May leaves 10 Downing Street to attend the weekly Prime Ministers' Questions session, at parliament in London, Wednesday, March 20, 2019. (Photo: AP)

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", she said.

Delaying Brexit to June 30 would bring "serious legal and political risks", the European Commission warned Wednesday in an internal briefing note ahead of an EU summit.

Britain has asked to postpone Brexit to that date, but the commission, the EU's executive arm, urged leaders to choose instead between a short delay to May 23 or a longer one to "at least until end 2019".