Rishi Sunak’s Rwanda deportation policy is doomed to fail, Suella Braverman has said as she piled fresh pressure on the Prime Minister over his strategy to stop small boats.

The former home secretary, who was sacked from her Cabinet job last month, warned that the “time for talk” on tackling illegal immigration is over.

The draft Bill compels judges to treat Rwanda as a safe country after the Supreme Court ruled the scheme was unlawful over risks to refugees.

The reality is and the sorry truth is that it won’t work and it will not stop the boats

The legislation, which must be voted on by Parliament, gives ministers the powers to disregard sections of the Human Rights Act.

But it does not go as far as allowing them to dismiss the European Convention on Human Rights, as hardliners including Mrs Braverman have demanded.

That prompted Robert Jenrick’s resignation as immigration minister just hours after Mr Sunak tabled the draft Bill, saying it “does not go far enough” and is a “triumph of hope over experience”.

Mrs Braverman on Thursday said that “ultimately this bill will fail”.

She told BBC Radio 4’s Today programme: “Taken as a whole and looking at the reality of the challenges that are involved in detaining people, removing people and getting them to Rwanda – this is a very litigious field and there are lots of legal frameworks that apply – the reality is and the sorry truth is that it won’t work and it will not stop the boats.”

Tweaks to the Rwanda plan would not be enough to get people on the plane to Africa, Mrs Braverman said, adding that the new legislation would still allow legal claims that could block flights and “clog up the system”, potentially for years.

“We can’t do half measures. We have to totally exclude international law – the Refugee Convention, other broader avenues of legal challenge,” she said.

Mrs Braverman, who said on Wednesday that the Conservatives faced “electoral oblivion in a matter of months” if they introduced emergency Rwanda legislation which is “destined to fail”, denied the Tories have a “death wish”.

But she said they are in a “very perilous situation”.

“The Prime Minister made the promise to stop the boats at the beginning of the year. We now need to deliver on that pledge,” she said.

“The time for talk, the time for slogans and promises is over. We need to show delivery and that’s what this debate right now is all about.”

She insisted she wants the Prime Minister to succeed, despite describing him as “weak” and “uncertain” in a scathing attack on his leadership after he sacked her.

But she said Mr Sunak would have to change course if he wants to lead the party into the next election.

Challenged over her actions and her controversial style, the ex-home secretary said she does not “shy away from telling people how it is”, even if “that upsets polite society”.

Mr Braverman’s outspokenness on the issue and Mr Jenrick’s dramatic resignation signals a growing rightwing rebellion that could threaten Mr Sunak’s premiership.

Cabinet minister Chris Heaton-Harris attempted to play down Tory divisions over the Rwanda policy following Mr Jenrick’s departure.

Asked if the vote on the Safety of Rwanda Bill would be treated as a matter of confidence in the Prime Minister, the Northern Ireland Secretary told Sky News that was a decision for the whips but “I can’t see why it would need to be because I think all Conservatives will vote for it”.

Asked if the Prime Minister would face a confidence vote, Mr Heaton-Harris told LBC: “I think it’s highly unlikely, very unlikely. I’d say vanishingly small.”