An influential cross-party group of MPs is moving to wrest the initiative over the Brexit process from UK Prime Minister Theresa May.

CNN has learned that they are planning to introduce legislation on Monday that would scupper the government's Withdrawal Bill and block a "no-deal" Brexit.

The word in the Westminster corridors Friday was that this unprecedented cross-party "insurgency" was gaining strength. The government's "Plan B" – which is due to be set out on Monday and debated in the House of Commons the following week – would be rendered null and void if the MPs legislation were passed.

After a week of upheaval over Brexit in the House of Commons and angry exchanges on the streets outside, Britain's democratic system is looking a bit shaky. (PA)

Among the MPs behind the measure is the Conservative Nick Boles and Labour's Yvette Cooper and Hilary Benn. However, they and other supporters of the legislation will need to work with the Speaker of the House to get parliamentary time for their proposal.

A critical part of the bill – dubbed European Withdrawal 3.0 – would postpone the UK's departure from the European Union on March 29 if parliament fails to agree on a way forward by then.

That is the day on which Article 50 – the timetable for the UK's withdrawal – expires. Any extension would have to be agreed by the other 27 members of the EU.

According to a research paper just published by the House of Commons library, the bill means that "the government would be compelled to request an extension of the two-year negotiating period under Article 50".

It says "the drafters of the Bill specifically contemplate an extension of just over nine months, from 29 March 2019 to 31 December 2019".

The government has insisted that the threat of a "no deal" Brexit is an important element in its negotiating strategy with the European Union.

Outside, rival protesters sounded off and squared off, with some aiming angry shouts of "traitor" at their opponents. (EPA)

Prime Minister Theresa May has consistently ruled out an extension of Article 50, though many commentators believe there isn't enough time for parliament to pass the necessary legislation to give effect to withdrawal by the end of March.

According to the leaked transcript of a conference call, the British Chancellor or Finance Minister, Philip Hammond, told business leaders last week that the MPs' initiative would be "a sort of ultimate backstop if the work the government is doing in seeking to find a way forward fails to deliver".

The news follows a week of upheaval over Brexit in the House of Commons and angry exchanges on the streets outside.

In the Commons chamber, Prime Minister Theresa May suffered the biggest defeat in Parliament's history over her European Union divorce deal, narrowly survived a no-confidence vote the next day and was left scrambling for a workable new Brexit plan.

Outside, rival protesters sounded off and squared off, with some aiming angry shouts of "traitor" at their opponents. Brexit has divided Britain, and left the country's democratic system battered, if not broken.

In the Commons chamber, Prime Minister Theresa May suffered the biggest defeat in Parliament's history over her European Union divorce deal, narrowly survived a no-confidence vote the next day and was left scrambling for a workable new Brexit plan. (PA)

"We have become an international laughing stock: anxious, angry, uncertain, divided," opposition Labour Party lawmaker Chris Bryant said during Tuesday's EU debate, lamenting that politicians had "squandered two years" arguing about Brexit.

"Party politics has failed," Mr Bryant said.

Soon after he spoke, lawmakers rejected the deal Ms May's government had painstakingly negotiated with the EU by 432 votes to 202, the biggest margin of defeat any British government has ever suffered.

The next day, Parliament held a no-confidence vote in the government called by Labour.

Ms May sat stony-faced as Labour deputy leader Tom Watson savagely said she lacked "the empathy, the ability and, most crucially, the policy to lead this country any longer".

Ms May survived by fewer than 20 votes, and ended the week clinging to office, holding talks with allies and opposition politicians in an attempt to forge a "Plan B" that must be presented on Monday.

But Parliament's Brexit factions are still deadlocked, with competing plans and no clear majority for any of them. Steven Fielding, a professor of political history at the University of Nottingham, said Brexit has paralysed the UK's parliamentary system.

"I cannot think of a moment in modern British politics that is at all comparable," he said.

"Maybe when (Prime Minister Robert) Peel split with his own party over the Corn Laws in 1846.

"The whole point of Britain's parliamentary system used to be that – in contrast to continental (European) countries – we elect majority governments that make decisions.

"There was none of this messy compromise stuff ... And (now) it is failing." Britain's political crisis has been building since the 2016 Brexit referendum that resulted in a narrow vote – 52 to 48 percent – for Britain to leave the EU.

French Prime Minister Edouard Philippe gathered the ministers concerned in preparation for Brexit. (PA)

An election the following year – called to cement the power of Ms May's Conservatives – saw them lose their majority in Parliament, leaving her atop a fragile minority administration that struggles to pass legislation.

In a further complication, Brexit has split the main political parties, Conservatives and Labour, right down the middle.

Each party includes both pro-Brexit and pro-EU factions, divided into multiple sub-categories: clean-break "hard Brexiteers" who want a firm break with the EU; those who support keeping close ties to the bloc; and those who back holding a second EU membership referendum.

Ms May will show lawmakers her revised Brexit blueprint on Monday, and they will try to amend it and seize control of the Brexit negotiations during a debate in the House of Commons on January 29.

But is not clear what policy, if any, can find majority support. Meanwhile, Britain draws ever closer to an abrupt and potentially chaotic "no-deal" departure from the bloc on March 29.

Watching this epic political spectacle lurching forward each day, Britons are bored, bemused, angry and afraid – sometimes all at the same time.

Brexit has divided Britain, and left the country's democratic system battered, if not broken. (AP)

And the country is still as divided over its relationship with Europe as they were during the referendum campaign.

"Brexit or a penalty shootout? The choice is yours ... I know where we'll be," soccer commentator Gary Lineker said Wednesday night when Ms May's latest televised speech collided with the end of an exciting FA Cup game.

All week, pro-Brexit and pro-EU demonstrators gathered outside Parliament in London to trade chants, arguments – and, in a small number of cases, abuse.

Anti-Brexit campaigner Jane Keane said Parliament's impasse was "a democratic crisis," and urged lawmakers to order a new referendum on Britain's EU membership.