MP Theresa May has been granted an extra two weeks to come up with a Brexit solution after talks with EU leaders.
The UK’s departure date is set to be extended from 29 March to 12 April.
If May can get her withdrawal deal through Parliament next week that date will be pushed back to 22 May to give time to pass the necessary legislation.
If she can’t get the deal through the UK will have to propose a Brexit plan B by 12 April for EU leaders to consider.
European Council President Donald Tusk said all Brexit options would remain open until then.
“The UK government will still have a choice between a deal, no deal, a long extension or revoking Article 50,” he said.
“The 12 April is a key date in terms of the UK deciding whether to hold European Parliament elections.
“If it has not decided to do so by then, the option of long extension will automatically become impossible.”
Mrs May ruled out revoking Article 50, which would cancel Brexit, and she also said “it would be wrong” to ask Britons to vote for candidates for the elections to the European Parliament three years after they voted to leave the EU.
The UK’s departure date is still written into law as next Friday, 29 March.
Mrs May is expected to table secondary legislation – that has to go through the Commons and the Lords by next Friday – to remove that date from UK law.
But Downing Street sources say an agreement with the EU to extend the Brexit deadline would be a piece of international law and would take precedence even if Parliament rejected it.
Mrs May said MPs had a “clear choice”.
Speaking on Thursday, after waiting for the 27 other EU countries to make their decision at a summit in Brussels, the prime minister said she would now be “working hard to build support for getting the deal through”.