Boris Johnson has warned that Theresa May’s “cheat” Brexit plans would leave the UK in “manacles” and lead to the dominance of the far right and far left in British politics.

The ex-cabinet minister made the claims as he also launched a broader attack on the prime minister’s policies on Brexit, crime and taxation on the third day of Conservative conference in Birmingham.

The speech in front of a packed-out hall of supporters is widely seen as a pitch for the support of Tory members, ahead of an expected leadership bid in the near future.

Ms May’s office were apparently spooked enough by his support to try and launch a PR counter offensive on Tuesday morning, but with her own MPs meeting Mr Johnson in front of the cameras ahead of his speech it seemed to have had little impact.

In his most stinging attack yet on Ms May’s plans for Brexit, he said: “What the Chequers proposals show is that the United Kingdom, for all its power and might and network of influences around the world, for all its venerable parliamentary history, was ultimately unable to take back control.

“And instead of reasserting our ability to make our own laws, the UK will be effectively paraded in manacles down the Rue de la Loi like Caractacus.”

Caractacus was a first-century British chieftan who led the resistance against the Roman Empire, but was ultimately defeated, captured and taken to Rome as a war prize.

The ex-foreign secretary went on to warn that Ms May’s Brexit deal would embolden those who are campaigning for a second referendum and was a “recipe for further acrimony”.

He said: “If we cheat the electorate – and Chequers is a cheat – we will escalate the sense of mistrust.

“We will give credence to those who cry betrayal, and I am afraid we will make it more likely that the ultimate beneficiary of the chequers deal will be the far right in the form of UKIP and therefore the far left in the form of Jeremy Corbyn.”

Mr Johnson won loud applause when he suggested that the PM risked being prosecuted under a 14th century law saying that “no foreign court or government shall have jurisdiction in this country”.

He rejected as “total fantasy” the idea that it would be possible to “bodge” Brexit now and then negotiate a better deal after leaving in March 2019.

The Uxbridge MP went on to warn that Ms May’s blueprint – which ties Britain to a common rulebook with the EU for trade in goods – would be “politically humiliating for a £2tn economy” and would prevent the UK from making its own laws and subject it to the directives of Brussels.

Queues to enter the speech venue reached far around the corridors of the conference venue where Mr Johnson was speaking, with some of his admirers turning up two-and-a-half hours early for his appearance.

It came after days in which he has already launched a series of attacks on the prime minister and her Brexit plan, but on Tuesday he went further taking a swipe at her broader agenda.

On crime he said: “We Conservatives know that it is only a strong private sector economy that can pay for superb public services. And that is the central symmetry of our one nation Toryism.

“Because it is only by making sure that the streets are safer – and let’s bring back stop and search incidentally, and end this politically correct nonsense that has endangered the lives of young people in our capital.

“It is only by putting in the infrastructure that enables people to live near their place of work; it is only with a properly funded NHS...that you can give people the peace of mind they need.”

Ms May was responsible for a rolling back in the stop-and-search approach to policing while home secretary and has held to the policy as prime minister, with some pointing its absence as being responsible for a rise in knife crime.

Iain Duncan Smith, a former leader of the party, said Tory chiefs had to recognise when the membership is “saying something to you” and that Mr Johnson’s speech should be seen as a message to government.

Former cabinet ministers Owen Paterson and John Redwood said Ms May had to understand that mainstream opinion in the party was bitterly opposed to her plan. But not everyone was quite as impressed,

Conservative former Brexit secretary David Davis said of Mr Johnson’s event: “It was a good speech, nice and clear.”

Asked what impact it would have on Ms May’s keynote speech on Wednesday, he said: “It’s a different speech, she’s the prime minister, she’s got to give a serious speech about the future of not just Brexit but all the other elements of the domestic strategy – which of course Boris was talking about too. She’ll make a good speech.”

Mr Davis played down claims that Mr Johnson’s decision to come to conference represented a leadership bid, saying: “We’ve had speeches all week from the chancellor, the foreign secretary, from all sorts of people and they set the scene.”

Others in the crowd also caveated their support. David Drew, who sits on Test Valley Borough Council, said: “Boris is a great performer. He obviously wowed the crowd.

“I was a little concerned when he got such applause for saying we should chuck Chequers because I think it’s a starting site.”

Asked if Mr Johnson would be the next party leader, he replied: “I doubt it. I’m not even sure he will get on the ballot paper.”

Carol York, a party member from Mid Sussex, said it was a “good, rousing speech”.

She added: “It was very good and he supported Theresa May as well.”