BORIS Johnson’s Brexit policy was in disarray last night after 21 Tory rebels joined the opposition parties to inflict a humiliating Commons defeat on the UK Government to block a no-deal exit.

The embarrassing setback came on the day the Prime Minister lost his parliamentary majority with the defection of the former Conservative minister Philip Lee, who dramatically crossed the Commons floor to join the Liberal Democrats.

Outside Westminster hundreds of protesters gathered, chanting "Boris out," while inside MPs engaged in a passionate debate on Parliament’s role on Brexit.

After three hours, the so-called Rebel Alliance’s attempt to take control of Commons business for Wednesday passed to rousing cheers in the chamber by 328 votes to 301; a majority of 27.

Some 21 Tory rebels defied their leader, including Ken Clarke and Philip Hammond. All faced automatic expulsion.

Following the defeat, the Government laid a motion to hold a snap election; set for October 14.

Mr Johnson will need opposition numbers to pass the motion but Labour, the SNP and the Liberal Democrats said they would only consider backing such a poll once a no-deal option was ruled out. “Get the bill through first,” declared Jeremy Corbyn.

Opposition politicians will today vote to pass a law to try to push Brexit Day back from October 31 to January 31.

During Commons exchanges, the Prime Minister insisted under no circumstances would he be forced “to beg for yet another pointless delay; if that happens, all the progress we have been making will have been for nothing”.

Mr Johnson denounced the move to delay Brexit further as “Jeremy Corbyn’s surrender bill,” and after the Government defeat told MPs: "The consequences of this vote tonight means Parliament is on the brink of wrecking any deal we might be able to get in Brussels.”

The SNP’s Ian Blackford urged the Tory leader to act like a prime minister, declaring: “The Government must respect the sovereignty of the House, must allow the bill to be enacted…Yes, let us have an election but let us have one that respects the democracy of this House.”

Following the vote, Nicola Sturgeon tweeted: "Very good result in the Commons tonight (has a Prime Minister ever before lost his/her first Commons vote?).

"Next step now is to get the 'no deal' threat off the table by passing the Bill being introduced tomorrow...and then let's have a General Election. The SNP is ready for it!" added the First Minister.

Opening the emergency debate, Sir Oliver Letwin, the former Cabinet Office Minister, said: "Over the last six weeks the Government has not produced a single indication of any viable proposal to replace the backstop by any alternative likely to prove acceptable to the EU.

"The likelihood of the Government reaching a deal at the council meeting on October 17 and 18 on the terms the Government itself has set is accordingly slight."

The Tory backbencher added this was the last week Parliament would have to block a no-deal exit on October 31, noting: "It's decision time.

"If MPs across the House want to prevent a no-deal exit on October 31 they will have the opportunity to do so if, but only if, they vote for this motion this evening."

Commons Leader Jacob Rees-Mogg warned the motion "risks subverting Parliament's proper role" in scrutinising the executive.

He described those supporting the emergency motion as an "Illuminati who are taking the powers to themselves".

Mr Rees-Mogg went on: "It is not, however, for Parliament to undertake the role and functions of the executive.

"Constitutional convention is that executive power is exercised by Her Majesty's Government which has the democratic mandate to govern.

"That mandate is derived from the British people and represented through this House.

"When we look at this constitution we are protected by our rules and our orders and by our conventions."

The Commons Leader added: "It is those rules, those laws, those conventions that protect us from the winds of tyranny."

The SNP’s David Linden asked if the Government would not stop an anti-no-deal law getting Royal Assent.

Mr Rees-Mogg replied: "The law will be followed. This country is a country that follows the rule of law and its Government assiduously follows constitutional conventions, unlike some other members of this House."

The 21 rebel Tories included not only Mr Clarke and Mr Hammond but former ministers Rory Stewart, David Gauke, Greg Clarke, Sir Oliver and Sir Nicolas Soames.

Later, a Downing Street spokesman said: "The Chief Whip is speaking with those Tory MPs who did not vote with the Government this evening. They will have the whip removed."