Several Tory MPs have rebelled against the Prime Minister over Brexit and voted against the government in a crucial motion in Parliament.
MPs voted by 328 to 301 in support of a motion, put forward by Tory rebel Oliver Letwin, to take over the agenda in the House of Commons. It means they can now bring forward a bill on Wednesday that would force Mr Johnson to delay Brexit unless MPs back a new deal or vote for a no-deal Brexit.
Mr Johnson immediately said he would be seeking to call a general election on 14 October.
Later, a spokesman said that conservatives who voted against UK government would be expelled from the party.
Under the Fixed Term Parliament Act the prime minister needs a two-thirds majority in Parliament if he is to call an election before 2022. It is unclear whether Labour will vote in favour of a general election, although Jeremy Corbyn has been baying for one.
During the debate, Mr Letwin spoke disparagingly about Downing Street’s strategy of threatening the European Union that he would leave without a deal if they did not accept a compromise on the Irish backstop.
Mr Letwin said: “Far from threatening the EU, the threat is to our country. He is like someone standing on one side of the canyon shouting at someone on the other side of the canyon that if they do not do what he wants him to do then he will throw himself into the abyss….and he will take the rest of us with him…that is not a credible negotiating strategy.”
But the Leader of the House of Commons, Jacob Rees-Mogg, hit back and said the motion which was being debated was “constitutionally irregular.”
Mr Rees-Mogg said: “The Prime Minister has said this government is absolutely committed to leaving the European Union by 31 October. The referendum was the largest democratic mandate in the nation’s history. It was a historic vote. But instead of backing the Prime Minister and giving him the best chance of getting the best deal we see ourselves debating a motion which is seeking to subvert Parliament’s role.”
Later Mr Rees-Mogg claimed the government had to negotiate on behalf of the nation and to ignore that fact was to fall foul of the "winds of tyranny".
He was then challenged by an opponent who asked him why he had voted against Theresa May’s withdrawal deal.
Mr Rees-Mogg replied: “The deal (she negotiated) is dreadful and that is why the Prime Minister is getting a better one.”
Jeremy Corbyn said a no deal Brexit would “decimate our manufacturing industry”, would threaten the Good Friday Agreement in Northern Ireland and would bring “chaos” to Britain’s ports and airports.
He said Britain’s economy was already “fragile” and added: “Now is not the time to play Russian roulette with our economy.”
Mr Corbyn quoted Make UK, an umbrella group of 20,000 British manufacturers, who said leaving the EU without a deal was “the height of economic lunacy.”
But Bill Cash, a Tory MP and long-term Eurosceptic, said: "We must be allowed to govern ourselves. We do not govern ourselves and if we stay in this European Union we will never be able to do so."
Ken Clarke, another Tory rebel and a former Chancellor, said "the government is insisting on pursuing a policy which it knows Parliament is opposed to" and it would be "quite horrendous" for Parliament to be sidelined.
Labour MP Gordon Marsden referred to the Prime Minister as a "petulant man-child" who could not get his own way with Parliament.
Earlier in the day a Tory MP, Phillip Lee, defected to the Liberal Democrats in the middle of Mr Johnson's speech. The defection means the Tories have no longer a majority in Parliament, even with the support of the DUP.