Up to 400,000 asylum seekers will be ‘immediately detained’ and deported if Reform win the next general election.

Revealing new details of its pledge to tighten border controls, Nigel Farage’s Reform UK said all illegal migrants who arrived in the five years prior to the next election would be locked up.

It would include those who arrived by small boat or clandestinely in the backs of lorries, as well as those who claimed asylum using fake documents, the party said.

The figure would come on top of 600,000 deportations Reform last year indicated it would enforce, making a total of one million. 

A Reform government would also review all grants of asylum going back five years, leading to further deportations.

Anyone who claimed asylum after overstaying a visa would be detained and deported, the party’s new policy set out.

A third category of asylum seeker - those whose home countries are now deemed to be safe - would also be stripped of their visas and be eligible for removal.

The detention of such large numbers of people would pose a huge challenge as the current capacity of immigration removal centres is less than 3,000 beds.

But a Reform spokesman predicted many of those targeted by the new policy would choose to leave Britain voluntarily.

For those who remained the party would create ‘pop up’ detention centres, he added.

Reform UK’s home affairs spokesman Zia Yusuf accused Labour and the previous Conservative government of allowing Britain to be ‘invaded’ by asylum seekers.

‘For years, Tory and Labour governments have presided over an invasion of Britain,’ he said.

‘They have effectively operated an open borders policy.

‘Instead of upholding the law, they have rewarded those who broke it by entering Britain illegally.

‘Reform will reverse this.’

He added: ‘Today we announce that a Reform government will review the previous five years of asylum grants, and anyone who broke into the country illegally or overstayed on another visa will be stripped of their status and deported.

‘We will do what it takes to restore justice in Britain.’

The party said the review would see ‘leave to remain’ cancelled for anyone who fell into any of the three categories, along with their dependants’ permission to stay here.

They would be ‘given a period of time to leave the country’, after which they will be deported by Reform’s planned UK Deportation Command.

A Reform spokesman said: ‘Assuming a Reform UK Government is formed after a General Election in 2029, we would expect over 400,000 people to be in scope of this policy.

‘This is based on grants over the last two years, those currently in the asylum system, and those expected to enter it over the next three years.

‘Circa 55 per cent of asylum applicants arrived by small boat, clandestinely or without relevant documentation over the last five years - based on Home Office data - so the vast majority of people in scope will have their humanitarian status revoked.’

The spokesman added: ‘Those within the asylum system would be immediately detained and prioritised for deportation.’

The party has committed to taking Britain out of the European Convention on Human Rights and the 1951 Refugee Convention.

It would also pass new legislation, the Illegal Migration (Mass Deportation) Act, to allow removals to take place.

Previous legislation which allowed asylum seekers to be treated less favourably if they arrived by illegal routes was passed by the former Tory government in 2023.

But it has since been repealed by Labour.

It came as 602 small boat migrants reached the UK on Saturday, pushing this year’s running total past the 6,000 mark.

Nine boat-loads of migrants were picked up mid-Channel by Border Force vessels during Saturday and brought ashore at the Port of Dover.

It also means that since Labour came to power 70,701 migrants have crossed the Channel to reach Britain.

Shadow Home Secretary Chris Philp said: ‘Conservatives have already proposed a detailed borders plan to pull out of the ECHR and completely ban asylum claims by illegal immigrants - instead we would deport them within a week of arrival.

‘The Conservative’s Removals Force will deport 150,000 immigrants each year with no right to be here.

‘Reform is slowing catching up with our ideas - but without the detail that will ensure it works in practice.’