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Jeremy Corbyn’s offer to back the Prime Minister’s Brexit deal in return for a customs union is rejected by the Conservative chairman today.

Brandon Lewis said tying Britain to the European Union’s trading bloc rules would “not respect the referendum result” of 2016.

In an interview with the Evening Standard, Mr Lewis said the onus was on Mr Corbyn to support the Government if Theresa May came back with an agreement that protected jobs.

“Look, I would hope the Labour Party and all parliamentarians would back the Prime Minister’s deal,” he said.

“The problem with what Labour outlined is that would not allow us to do global trade deals and therefore doesn’t respect the referendum.”

If the scenery falls apart at next week’s Tory conference, Mr Lewis is the man who will be holding his head in his hands. The 47-year-old Conservative Party chairman is the “safe pair of hands” entrusted not only with preventing a repeat of the mishaps that befell Mrs May 12 months ago, but also for preventing civil war breaking out at a conference overshadowed by Brexit and by ministers jostling for the Tory leadership.

In his opening address on Sunday, he will boast that the number of under-25s attending this year’s conference is double last year’s tally, countering the grim reality that the Conservative membership is increasingly elderly. As part of overhauling “the oldest and most successful political party in the world” he will unveil the first “interactive” conference app, which will let the rank and file provide feedback during Cabinet ministers’ speeches.

Mid-term conferences are tricky, he admitted, but claimed: “I think they [the members] are much more united than we are given credit for. Ultimately the party will always come together and do what is right for the country.”

One headache is the inevitable beauty parade of ministers and backbenchers setting out their stalls as future leaders amid speculation that Mrs May could be forced from office.

“One of the great pleasures in serving in this particular Cabinet is we have such a wealth of talent,” observed Mr Lewis, deadpan. “We are very blessed with having so many brilliant people.”

But there was sincere admiration in his voice as he recalled how the PM reacted to a security breach during her keynote address last year when a prankster got within touching distance and handed her a fake P45.

“It was slightly surreal. But I thought the way the Prime Minister dealt with it really did show why she is so good. The calmness — she didn’t flinch — but also the humour she showed.”

What lessons have been learnt from that debacle, which climaxed in letters falling off the stage backdrop? “There are no magnets, no felt,” he replied.

He said someone setting up early that morning had brushed against the stage and the letters, which were pinned up, were knocked down. The culprit pressed them back into place, but they were loose. The foot-stomping and cheering in the hall during the speech caused vibrations that dislodged the loosest letters.

“It would be unfair on the people involved [to name them] but it wasn’t any of our staff,” Mr Lewis said.

One major challenge he faces next week is to stop Boris Johnson from hijacking the conference with his campaign against the PM’s Chequers proposals for Brexit. Mr Lewis claimed he was relaxed, saying it was all “part of the excitement of conference”.

But hovering over the two men is the official party inquiry into whether Mr Johnson broke conduct rules by writing a column that said women who wear the burka resemble “letter boxes” and “bank robbers”.

As the row developed, Mr Lewis tweeted that the former foreign secretary should apologise for the remarks.

The chairman would not comment on the investigation, which is not expected to conclude before the party conference. But he did not regret his call for an apology. He backed Johnson’s argument that Britain was a liberal country that should not ban burkas. “But,” he went on, “all of us as politicians have to be aware of the language we use.”

On the issue of Brexit, the party chairman claimed that opposition to the Chequers plan among party activists and branch officers was exaggerated. “Our membership is pretty pragmatic. When you talk to them about the detail in the White Paper, actually they are quite supportive of it.”

Did he think Philip Hammond, the Chancellor, was right to warn that a no-deal Brexit would be a disaster for the economy?

“I don’t work in hypotheticals,” he swerved. “I think there will be a deal.”

Mr Lewis, whose father left school with no qualifications and rose from delivery driver to owning a confectionery company, said he absorbed his father’s values.

“I think the reason I am a Conservative is that work ethos and entrepreneurial spirit of my dad,” he said. He did not follow his father into business, however, becoming a barrister “because the law just fascinated me”.

He joined the Conservatives aged 26 in 1997, just as most young people were fleeing a party routed by Tony Blair. He made his name on Brentwood council, leading the Tory group to victory, and became an MP by snatching Great Yarmouth from Labour.

Tomorrow he will fire the starting gun of the campaign to unseat Mayor Sadiq Khan from City Hall by announcing the result of the ballot to choose the next Conservative candidate for Mayor of London, from a shortlist of Shaun Bailey, Andrew Boff and Joy Morrissey.

He stressed that the winner will make “a positive pitch about what they will do for London”, implying no repeat of Zac Goldsmith’s 2016 campaign, which was criticised for negativity.

Mr Khan’s Achilles’ heel was delivery, he claimed. “He is not delivering on housing or crime, and he is the one who makes decisions. Many Londoners think he is not delivering on transport either. If you look at Sadiq’s record, he has failed.”