In a dramatic intervention in the Commons, the prime minister said defeat on his bid to ram the legislation through in just three days – the so-called programme motion – could see it scrapped altogether.
“If parliament refuses to allow Brexit to happen, and instead gets its way and decides to delay everything until January or possibly longer, in no circumstances can the government can continue with this,” he told MPs
“I must say the bill will have to be pulled and we will have to go forward to a general election.”
The threat raises the stakes enormously for the vote on the controversial fast-track timetable – which will follow if, as expected, MPs give backing in principle to the bill.
Unless the withdrawal agreement bill clears the Commons by Thursday, the prime minister will suffer the embarrassment of having to abandon his pledge of leaving the EU by 31 October.
In the only previous example of a programme motion defeat, on House of Lords reform, the Cameron government pulled the legislation rather than press on with no guillotine on debate.
However, Mr Johnson suggested he would do the same only if defeat was coupled with the EU agreeing a three-month delay – when a shorter extension, to allow ratification, is also possible.
It also remains unclear whether the prime minister could force an election if he tried, after Labour and other opposition parties blocked it last month.
Opening debate on the legislation, Mr Johnson said: “If we delay again I am afraid that we will miss an opportunity to heal the divisions between us and the paralysis will continue.”
And he added: “I will argue at the election ‘let's get Brexit done’ and the leader of the opposition will make his case to spend 2020 having two referendums: one on Brexit, and one on Scotland and the people will decide.
“There is another path and that is to accept as I have done that this deal does not give us everything we wanted.”
But the Liberal Democrats accused the prime minister of “childish blackmail” in a bid to “rush through this bad Brexit deal without proper scrutiny”.
There is a clear motive for No 10 to issue dark threats about an election – to strongarm both Tory MPs determined to deliver Brexit and Labour MPs who fear going to the polls under Jeremy Corbyn.
Previous anonymous warnings from Downing Street sources – notably that Mr Johnson would not request a Brexit delay last weekend, which he then did – have proved false.
“MPs shouldn’t be bullied into voting in favour of this ridiculously short timetable,” said Tom Brake, the Lib Dem Brexit spokesman.