One senior figure even claimed police would have to turn up outside Number 10 with a warrant in order to persuade him to leave. Meanwhile European Research Group chairman Steve Baker has told Express.co.uk Mr Johnson was well within his rights to defy MPs who he accused of “breaking constitutional norms”.
Mr Johnson is facing a showdown with MPs with the UK set to quit the bloc at the end of the month, with a new law passed last month - the so-called Benn Act - requiring him to request a further delay to Article 50 if he fails to agree a deal with Brussels by October 19.
Senior Tories told The Times Mr Johnson would refuse to budge even if he is found to be in contempt of court for ignoring the legislation.
They further suggested he would refuse to resign even if MPs passed a vote of no confidence in his Government and tried to replace him with a caretaker PM. Speaker John Bercow’s name has been discussed, sources added.
One senior figure added: “Unless the police turn up at 10 Downing Street with a warrant for the Prime Minister’s arrest, he won’t be leaving.”
The working assumption of pro-Remain MPs who have been working to prevent the UK leaving on October 31 without a deal in place was that Mr Johnson could be forced out if a caretaker Prime Minister could be shown to command majority support in the House of Commons.
However, this would depend either on Mr Johnson resigning - something he is thought to be unlikely to do - or the Queen giving him his marching orders, which would place the 93-year-old sovereign in an extremely awkward position.
No reigning monarch has sacked a Prime Minister since William IV dispensed with the services of Lord Melbourne in 1834.
A senior cabinet minister said: “Our opponents have flouted convention and there is nothing in the Fixed-term Parliaments Act that says you have to resign.
“The Queen is not going to fire the prime minister.
“She would dissolve parliament and let the people decide.”
Mr Baker said: “Boris is right to defy NOs who are breaking constitutional norms by refusing to vote for an election.
“As soon as possible, the Fixed Term Parliaments Act must go.”
The latest developments come before another momentous week in Westminster as Mr Johnson’s Government prepares to outline its domestic policy programme in the first Queen’s Speech since June 2017.
However, Ministers expect it to be voted down by the House of Commons, according to The Sunday Telegraph, dealing yet another defeat to Mr Johnson.
By Parliamentary convention, the Queen’s Speech is seen as a confidence vote in the Government, meaning if Mr Johnson loses he will be under even more pressure.
Stanley Baldwin, the last UK Prime Minister to lose a such vote in January 1924, resigned not long afterwards.
Downing Street will probably argue that the circumstances are exceptional, pointing to Parliament’s refusal to allow Mr Johnson to call a general election.
However, the Sunday Telegraph also suggested at least some of the 21 Tory MPs drummed out of the party for backing the Benn Act may vote with the Government.
One source within Westminster said the group’s intention was “not to bring down the Government”.
The insider added: “This group are, at heart still conservatives.
“So they are still focused on that aim and they would think carefully about doing anything that was not aligned with stopping no deal”.