Prime Minister Boris Johnson spent Friday frantically twisting arms to get wavering MPs behind his Brexit deal, with a looming vote in parliament teetering on a knife-edge.

The Conservative leader pulled off a major coup in agreeing a new divorce deal with the European Union on Thursday, with only a fortnight to go before Britain is scheduled to leave the bloc on October 31.

But the agreement must now be approved by the House of Commons, which is meeting on a Saturday for the first time since the Falklands War 37 years ago to debate the text.

Its fortunes - and Britain's immediate fate - rests in the hands of a few undecided MPs.

Political pundits suggest the vote could be exceptionally tight.

Johnson has no majority among MPs, every opposition party has come out against the deal and even his parliamentary ally, Northern Ireland's Democratic Unionist Party (DUP), says it cannot support the terms.

Johnson requires the support of 319 other MPs to guarantee victory - and claims he is confident of getting the numbers, as he spent the day meeting and calling wavering MPs before hosting the cabinet.

He must convince diehard eurosceptics in his own Conservative ranks, former colleagues he expelled from the party for seeking to block no-deal, and main opposition Labour MPs from Brexit-backing constituencies to have any chance.

Labour is ordering its MPs to vote against the deal but threatening no punishment if they vote in favour of it.

Several MPs spent Friday wrestling with their consciences as the more than three years of turmoil since the June 2016 EU membership referendum came to a head.

Johnson is expected to deliver a speech to parliament from 0830 GMT on Saturday, kicking off a day of debate that could last well into the evening.

Macron turns the screw

If the Commons rejects the deal, Johnson will be forced by law to ask the EU to delay Brexit, for what would be the third time. He has said he would rather be "dead in a ditch".

French President Emmanuel Macron piled on the pressure on MPs, saying he did not want to see a third delay to Britain's departure date now a new divorce deal has been struck.

"The October 31 date should be respected. I don't think that new deadlines should be given," he said at the EU summit in Brussels.

"We need to end these negotiations and get on negotiating the future relationship."

And Luxembourg's Prime Minister Xavier Bettel added: "There is no choice between Brexit or no Brexit: it's a choice between deal or no deal."

Johnson took office in July vowing to keep to the October 31 Brexit deadline, deal or no deal.

He pledged to renegotiate the most contentious elements of a divorce text agreed by his predecessor Theresa May with Brussels last year, which MPs rejected three times.

The compromise deal that was finally struck on Thursday has a new arrangement for keeping open the border between British Northern Ireland and EU member Ireland.

The DUP has said it cannot support the plans, as efforts to avoid checks on the Irish land border would lead to new trade barriers between Northern Ireland and mainland Britain.

Former PMs wade in

Former Conservative prime minister John Major (1990-1997) and his Labour successor Tony Blair (1997-2007) pleaded with MPs to back a second referendum, in a joint video ahead of Saturday's major "People's Vote" rally outside parliament.

"Whatever is the outcome, no deal or bad deal, it should not pass without the final say resting with the people," said Blair.

Major said Brexit was a "thoroughly bad idea" that risked breaking up the UK.

Sterling steadied around $1.29 Friday as dealers took a breather at the end of a dizzying week.

ETX Capital analyst Michael Baker said the market was "really gambling" on the vote and had "not priced in fully all scenarios -- so expect big moves".

Britain's eurosceptic newspapers backed Johnson's deal, which comes more than three years after Britons voted narrowly to leave the EU in a referendum that has left the country bitterly divided.

"Get real... take the deal!" said The Sun's front page, while the Daily Mail went for "He's done his duty. Now MPs must do theirs", and the Daily Express said "Just do it!"