Both contenders to be the UK’s next Prime Minister have vowed to toughen controls on immigration and both have backed the Conservative government’s controversial policy of sending migrants to Rwanda.

Former finance minister Rishi Sunak and foreign secretary Liz Truss are the last two standing in the battle to become Britain’s next PM after a revolt over Boris Johnson’s scandal-ridden administration forced him to announce he will stand down.

Mr Sunak has said he would tighten the definition of who qualifies for asylum and introduce a cap on refugee numbers, while Ms Truss has said she would extend the UK’s Rwanda asylum plan and increase the number of Border Force staff.

More than 14,000 migrants have crossed the English Channel to the UK on small boats so far this year.

In an attempt to deter the crossings, in April the government announced it would send some asylum seekers deemed to have entered the UK illegally to Rwanda to claim refuge there.

However, no asylum seekers have been sent to the east-African country yet following a series of legal challenges.

The UK stands to lose the £120 million it has paid to Rwanda if the plan is ruled unlawful by the courts at an upcoming hearing.

Both leadership hopefuls said they would explore similar deals with other countries.

Ms Truss recently told media that the Rwanda policy was the right approach and that she was determined to implement it.

She said that if she became PM, she would increase Border Force staffing from 9,000 to 10,800.

Mr Sunak has also pledged to do “whatever it takes” to make the Rwanda scheme work and described the UK’s migration policy as “broken” and “chaotic”.

His plans would see the UK re-assessing aid, trade terms and visa options on the basis of a country’s willingness to co-operate with the return of failed asylum seekers and offenders.

He has also promised to give Parliament control over how many come to the UK by creating an annual cap on the number of refugees accepted each year, though this could be changed in the case of emergencies.

And he said he would introduce enhanced powers to detain, tag and monitor those entering the UK illegally.

“Right now the system is chaotic, with law-abiding citizens seeing boats full of illegal immigrants coming from the safe country of France with our sailors and coastguards seemingly powerless to stop them,” he said.

Meanwhile, the opposition Labour shadow home secretary Yvette Cooper criticised the pair’s proposals, saying they were wasting taxpayers’ money on the Rwanda scheme.

“The Conservatives have been in power for 12 years. It beggars belief that they claim to be the ones to sort things out when they have both failed for so long,” Ms Cooper said.

Last month, 47 people were told they would be flown to Rwanda, with a flight booked for 14 June. But after a series of legal challenges the flight was cancelled.

Another flight has not yet been scheduled.

Recently, a UK parliamentary committee cast doubt on the effectiveness of the scheme, saying there was no evidence it would stop people crossing the English Channel.

Conservative Party members are due to start receiving ballot papers this week and the winner will be announced on 5 September.