The former minister warned that backtracking on plans to overhaul the current system could hand the keys to No10 to Reform UK or the Tories, with both parties vowing to implement tougher changes to the system.

In a pamphlet from think tank Policy Exchange, Mr Johnson told the current Home Secretary: “Don’t listen to your Labour colleagues – press ahead.

“When you’re doing something that really needs to be done, particularly on illegal immigration, you always get a kickback, and she’s got to carry on.”

For the pamphlet, Policy Exchange interviewed more than a dozen former Home Secretaries on a range of topics, including terrorism, policing and Britain’s borders.

Last month, more than 80 Labour backbenchers wrote to Andy Burnham urging him against “losing progressive voters” by supporting the Home Secretary’s migration reforms.

Despite previously appearing critical of Ms Mahmood’s reforms, Mr Burnham is now widely expected to back the bill.

Mr Johnson said the more Ms Mahmood listens to backbenchers, ‘the worse it will be’ for Labour.

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The former Greater Manchester Mayor believes the reforms would make the immigration system fairer for both asylum seekers and local communities.

Under Ms Mahmood’s current plans, migrants would have to wait twice as long to gain indefinite leave to remain, with the qualifying period increasing from five years to 10.

She said the changes would apply retrospectively to people already in the UK to avoid a wave of claims from migrants who arrived after the coronavirus pandemic.

One option reportedly being considered is exempting some migrants already in Britain from having to wait a decade, while another would create exemptions for some groups, such as social care and health workers.

Mr Johnson said the Home Secretary was ‘right’ to model changes to the migration system on Denmark

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Mr Johnson said the Home Secretary was “right” to model changes to the migration system on Denmark.

Addressing the potential consequences at the ballot box, the former Home Secretary said: “Pictures of people coming illegally into this country, people feel really, really strongly about it, and it’s no good suddenly thinking ‘We’ve done this to death, let’s move on’.

“We need to have the right policies to address it, or someone else will.

“This is Shabana’s main argument – ‘If we don’t do it there’s a very, very different approach from a very different party and they’ll end up in government’.”

The calls for the Home Secretary to press ahead with her migration reforms come as the eye-watering cost to taxpayers of detaining and moving illegal migrants within the UK and overseas was laid bare.

‘Pictures of people coming illegally into this country, people feel really, really strongly about it,’ Mr Johnson declared

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According to new figures released by the Home Office, a total of £185.5 million was spent between June 2025 and May 2026 on transporting and housing people held in immigration detention and Border Force custody.

The spending covers a range of services, including moving detainees between prisons, police stations, hospitals and short-term holding facilities.

The statistics, first shared with The Sun, also include the running costs of Immigration Removal Centres and escorting migrants to deportation flights.

The figures have prompted criticism from campaigners and opposition politicians, who have accused the Government of wasting taxpayers’ money.

John O’Connell, of the TaxPayers’ Alliance, said the Home Office needed to “pull the handbrake” on what he described as “eye-watering waste”.

Meanwhile, Shadow Home Secretary Chris Philp criticised the expenditure, calling it “a catastrophic waste of taxpayers’ hard-earned money”.