British Prime Minister Theresa May on Sunday warned lawmakers against voting down her deal, saying there would be "uncharted waters" ahead.
May has come under fire from huge sections of her own Conservative Party over her deal and is facing a revolt ahead of Tuesday's scheduled vote on her deal in the House of Commons.
May has been meeting with Tory rebels and ministers all week in an attempt to find a way through this particular obstacle of the Brexit puzzle, which has divided her party and the country.
"If you're going to have a referendum, that is going to affect the foundation, the constitution of our country forever, you better do that within the law", she says.
Barclay said Britain would enter "uncharted waters" if it loses the vote, but May could stay on as prime minister.
Media reports said May is under pressure from her cabinet to delay the vote and fly to Brussels to secure more concessions ahead of a planned summit with 27 fellow European Union leaders on Thursday and Friday.
"I believe Jeremy Corbyn getting his hands on power is a risk we can not afford to take", she added.
EU supporters will be pinning their hopes on a European Court of Justice ruling on Monday on Britain's right to unilaterally halt Brexit in its tracks.
The UK PM office at 10 Downing Street also confirmed that the historic vote would go ahead on Tuesday, according to the Financial Times.
Under the backstop arrangements, which will govern the gap between the end of the transition period in December 2020 and the new treaty on our Future Relationship, we would be bound indefinitely by EU-imposed rules.
She is under attack from more strident Brexit backers in her party as well as europhiles who want either a second referendum or a pact that maintains stronger EU-UK ties than the one offered by May.
Former Foreign Secretary Boris Johnson has odds of 8/1 following his repeated public bashing of Mrs May's plans.
Several MPs, including the parliamentary leader of the Northern Irish DUP Nigel Dodds, former Brexit minister Dominic Raab and former work and pensions minister Esther McVey called for May to renegotiate with Brussels. And if May is aiming to go back to Brussels to ask for changes to the divorce agreement, the summit next week - two days after the House of Commons votes - would be the ideal time to do it.
In an extreme circumstance, the Queen could ask the Labour leader to form a minority government instead.
"What we would urge [May] to do is either call a general election - because she wouldn't have the confidence of Parliament to carry on as prime minister", Rebecca Long-Bailey, Labour's business spokeswoman, told the BBC.