Highlights Conservative MP Phillip Lee defected to pro-European Liberal Democrats

Boris Johnson no longer has a majority in the 650-seat chamber

The defection does not automatically bring down the government

Prime Minister Boris Johnson on Tuesday lost his working majority in parliament ahead of a showdown with rebel MPs over Brexit that could lead to a snap election within weeks.

Johnson condemned a plan by lawmakers to block his Brexit strategy as "surrender" and said it would undermine his intention to negotiate a new divorce deal with the EU.

He said the move by opposition MPs and members of his Conservative party to try to delay Brexit beyond October 31 if he cannot agree exit terms with Brussels was like "running up the white flag".

Ahead of a first vote in the House of Commons on Tuesday evening, Johnson said: "There are no circumstances in which I will ever accept anything like it".

His aides had already warned that defeat would force him to call a snap election ahead of a crucial EU summit on October 17-18 -- and a mere fortnight before Brexit.

The rebels believe they have the numbers to force through the plan, which is backed by the main opposition Labour party and could delay Brexit to January 31.

In a theatrical show of defiance, Conservative MP Phillip Lee crossed the floor of the Commons while Johnson was making his statement, to defect to the pro-European Liberal Democrats.

As a result, the prime minister no longer has a majority in the 650-seat chamber -- but the defection does not automatically bring down the government.

This can only happen if the government loses a formal confidence vote.

On a day of high drama, an Edinburgh court meanwhile heard a legal challenge against Johnson's decision to suspend parliament next week for more than a month, which critics said was a bid to silence MPs.

The heightened political tension sent the British pound tumbling on Tuesday to its lowest level against the dollar in almost three years.

Delaying Brexit

Johnson took office less than six weeks ago, after his predecessor Theresa May was forced out over her failure to get her Brexit divorce deal through parliament.

From the start, he faced opposition from his own MPs who fear his threat of leaving the EU without an agreement with Brussels risks severe economic disruption.

Former finance minister Philip Hammond is among those who have joined with Labour to draw up legislation that could force the delay.

They will first try to make room in the parliamentary agenda for a debate of the bill by putting forward a motion set to be voted on by MPs on Tuesday evening.

If they succeed, they will introduce their bill on Wednesday and seek to get it through before parliament is suspended next week.

'No concrete proposals'

Johnson has rejected the divor

ce deal on the table but insists he wants to reach an agreement with Brussels to ease the end of Britain's 46-year-old EU membership.

EU leaders have refused to reopen the current Brexit text but Johnson insists progress is being made, saying that only with a credible threat to walk away will he secure a new deal.

But critics note that there are no formal negotiations with Brussels, and both sides have stepped up preparations for a disorderly divorce next month.

A spokeswoman for the European Commission said Tuesday that it had yet to see any "concrete proposals" from London on how it wants to change the existing deal.

Johnson revealed that he would meet Irish prime minister Leo Varadkar for the first time in Dublin next week to discuss Brexit.

Johnson has received a boost in the opinion polls by his assertive action against parliament over Brexit.

An early election could give Johnson a majority, although it is also a big risk, as the political landscape was deeply fragmented by the 2016 referendum.

Johnson would need the support of Labour to call a snap poll, as the law requires the backing of two-thirds of MPs.

Labour leader Jeremy Corbyn has repeatedly called for an election and warned that if the legislative route fails, he may try to force one by calling a confidence vote in the government.

But many Labour MPs also fear a trap.

Johnson's aides insist any election would be held before Brexit, but some of his opponents fear he could change the date at the last minute to after October 31.

This would leave parliament powerless to stop a "no deal" Brexit.