British Prime Minister Theresa May faces a fight for her political life this week in a parliamentary vote that will decide the fate of her Brexit divorce deal.

The text defining terms on which the island nation leaves its main trading partner after 46 years is the most important to face the House of Commons in years.

A big loss could spark immediate challenges to May from both within her Conservative Party and the opposition Labour party.

It would also leave the tortuous Brexit process in a state of flux -- and raise the prospects of a no-deal scenario -- less than four months before the March 29 departure date.

Media reports said May was under pressure from her cabinet to try to salvage the deal by delaying the vote and flying to Brussels to seek more concessions ahead of a planned summit with 27 fellow EU leaders on Thursday and Friday.

But Brexit Secretary Stephen Barclay told the BBC on Sunday: "The vote is going ahead."