Boris Johnson fails to challenge Theresa May in his big conference speech after undermining her Brexit plans

Foreign Secretary threatens to ‘blast into orbit’ Jeremy Corbyn

Boris Johnson delivers his speech on the third day of Conservative Party Conference in Manchester (EPA)

Boris Johnson has pulled back from openly challenging Theresa May after days of undermining her, instead insisting she will deliver “a great Brexit deal”.

The Foreign Secretary used his showpiece conference speech to heap praise on the Prime Minister, saying “the whole country owes her a debt for her steadfastness”.

He told the Tory faithful that he and the rest of the Cabinet agreed with “every syllable” of Ms May’s Brexit stance – despite setting out his own, different red lines last weekend.

Many senior Conservatives were furious, calling for Mr Johnson to be sacked for his disloyalty – while others believed he could stage a dramatic resignation and pose as a Brexit martyr.

But, speaking in Manchester, he stepped into line, praising the Prime Minister for having “won” the election, despite destroying the Conservatives’ Commons majority.

“She won more votes than any party leader and took this party to its highest share of the vote in any election in the last 25 years,” Mr Johnson said.

“The whole country owes her a debt for her steadfastness in taking Britain forward, as she will, to a great Brexit deal, based on that Florence speech on whose every syllable, I can tell you, the whole Cabinet is united.”

The speech was received warmly – but not ecstatically – by the party activists and was peppered with his traditional jokes, gibes and colourful language.

Brexit critics were told to “stop treating the referendum result as though it were a plague of boils or a murrain on our cattle or an inexplicable aberration by 17.4m people”.

“It is time to be bold, and to seize the opportunities, and there is no country better placed than Britain,” the Foreign Secretary argued.

He boasted that, among British exporting triumphs, was a programme sold to Cambodia called Neak Neng Klay Chea Sethey – or Who Wants To Be A Millionaire?.

“And it is thanks to the triumph of conservative values you are allowed to become a millionaire in Cambodia without being despatched for re-education by some Asiatic John McDonnell,” Mr Johnson joked.

Hailing Britain’s “growing space programme”, he turned on Jeremy Corbyn, saying: “I have a candidate for the first man we gently blast into orbit and that is the superannuated space cadet from Islington.

“I know he has an innocent and vole-trousered air but his domestic policies would rack up unfair debts for our children and grandchildren and his foreign policies would imperil not just this country but our friends and neighbours as well.”

Mr Johnson finished by quoting Winston Churchill, framing Brexit as like the Second World War, telling the faithful: “We are not the lion. We do not claim to be the lion.

“That role is played by the people of this country. But it is up to us now – in the traditional non-threatening, genial and self-deprecating way of the British – to let that lion roar.”

The Prime Minister was not present for Mr Johnson’s speech, but used a series of broadcast interviews to insist her decision not to sack him was a display of “strong leadership”.

“Weak leadership is having a cabinet of yes men, weak leadership is having a team of people who only agree with you,” Ms May said.

“Actually, strong leadership is about having a diverse range of voices around the cabinet table, who then come together, who discuss the issues and then come up with the answer.”