By Alan McGuinness, political reporter
Theresa May is facing the prospect of being offered a Brexit delay of up to a year at an emergency EU summit in Brussels.
The prime minister has been pushing for a delay to the end of June, with the possibility of Britain leaving at an earlier date if her Brexit deal is approved.
But her hopes look set to be dashed, having already been granted one short extension to the process.
In a letter to the remaining 27 EU member states, European Council President Donald Tusk said there was "little reason to believe" Mrs May's deal, which has already been defeated three times, could be ratified by the end of June.
Instead he said the European Council should discuss a longer extension, such as a "flexible extension" lasting "as long as necessary and no longer than one year".
The EU27 need to unanimously agree to any Brexit delay, which would see Britain avoid leaving without a deal on Friday.
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Mr Tusk wrote: "The flexibility would allow to terminate the extension automatically, as soon as both sides have ratified the withdrawal agreement.
"The UK would be free to leave whenever it is ready.
"And the EU27 would avoid repeated Brexit summits.
"Importantly, a long extension would provide more certainty and predictability by removing the threat of constantly shifting cliff-edge dates.
"Furthermore, in the event of a continued stalemate, such a longer extension would allow the UK to rethink its Brexit strategy."
Mr Tusk added that that "neither side should be allowed to feel humiliated at any stage in this difficult process".
Before her trip to Brussels, the PM will face Labour leader Jeremy Corbyn at PMQs from noon.
The cross-party talks between both sides, which are aimed at finding a compromise agreement to break the impasse and get a deal through Parliament, are certain to feature in their weekly clash.
Discussions are set to resume on Thursday, with no breakthrough thus far.
Labour claim there has yet to be a "clear shift" in position from Downing Street.
Once she arrives in Brussels, it is expected that Mrs May will sit down for talks with Mr Tusk.
EU leaders will then gather for discussions with European Parliament president Antonio Tajani, before the PM addresses them and makes the case for a shorter Brexit delay.