Those who refuse to back Theresa May’s Chequers blueprint for Brexit are “playing politics” with the UK’s future, the Prime Minister has said.

In an interview with the Sunday Times ahead her party conference in Birmingham, Mrs May set out her political agenda, and signalled she had a “long-term” job to do as PM.

She also announced plans aimed at bolstering her position, announcing measures to crack down on foreigners buying homes and proposals for a nationwide festival in 2022 – the year of the next scheduled general election.

But ex-foreign secretary Boris Johnson has lobbed a political hand grenade at Theresa May as the Tory conference begins, branding her Brexit plan “deranged” and “preposterous”.

In remarks that will fuel speculation about Mr Johnson’s leadership ambitions, he highlighted a key distinction between himself and Mrs May: “Unlike the Prime Minister, I campaigned for Brexit.”

In an interview with the Sunday Times, Mr Johnson said the UK should build a bridge to Ireland and put the HS2 rail line on hold to focus on a high-speed link in the north of England.

He branded Mrs May’s call for a facilitated customs arrangement – part of the Chequers plan to break the impasse in Brexit talks – “entirely preposterous”.

Suggesting he may be able to strike a better deal than Mrs May, he told the newspaper: “Unlike the Prime Minister, I fought for this, I believe in it, I think it’s the right thing for our country and I think that what is happening now is, alas, not what people were promised in 2016.”

Setting out an alternative policy platform as the Conservative Party conference began in Birmingham, the former cabinet minister said: “I think we need to make the case for markets.

“I don’t think we should caper insincerely on socialist territory. You can’t beat (Jeremy) Corbyn by becoming Corbyn.”

Mrs May used her own interview with the Sunday Times to set out her political agenda.

Under her plans, people and businesses who do not pay tax in Britain will face a surcharge of between 1 per cent and 3 per cent when they buy a property, with the money funding measures to tackle rough sleeping, the newspaper said.

Signalling that she intended to remain in Number 10 for years to come, she said: “There’s a long-term job to do.”

She added: “It’s not just about Brexit, it’s about the domestic agenda as well.

“I think we’re at a very important and historic moment for the UK. There are real opportunities for the UK outside the European Union.”

Setting out her plans for a festival in post-Brexit Britain, she said: “We want to showcase what makes our country great today.

“We want to capture that spirit for a new generation, celebrate our nation’s diversity and talent, and mark this moment of national renewal with a once-in-a-generation celebration.”

Mrs May also told the Sun on Sunday that she was “not bluffing” when she said “no deal is better than a bad deal” when it comes to leaving the EU.

“I believe that we can get a deal,” she added. “I believe we can get a good deal and that’s what we are working for. But nobody should be in any doubt.”

The Tory gathering in Birmingham has been marked by a deepening rift over Brexit policy.

The party was also hit by an embarrassing security gaffe as a flaw in the official conference app allowed access to the contact details of Cabinet ministers and senior MPs.

Tory chairman Brandon Lewis apologised for the breach of security and the UK’s data watchdog said it would make enquiries about the case.

Activists and journalists heading to the conference discovered the major security problem in the official app which many use to keep track of events.

Mr Lewis said the “technical issue” had been resolved but “we are investigating the issue further and apologise for any concern caused”.

The Information Commissioner’s Office said it would be “making enquiries with the Conservative Party” and “organisations have a legal duty to keep personal data safe and secure”.

The profiles of former foreign secretary Mr Johnson and Environment Secretary Michael Gove were among those reportedly accessed.