Settlement, also known as indefinite leave to remain, gives a person the right to live, work and study in the UK for as long as they like and apply for benefits if they are eligible.

The Home Office has said its figures show net migration added 2.6 million people to the UK population between 2021 and 2024, and around 1.6m people could settle in the UK between 2026 and 2030.

The government has based many of its reforms on policies pursued by Labour’s sister party the Social Democrats in Denmark and which the Home Office believes has led to a substantial reduction in migration.

Mahmood’s intention to apply the new rules to migrants who are already in the UK rather than just to those who arrive in future was denounced this week by Labour’s former deputy leader Angela Rayner as “un-British”.

On Wednesday, Downing Street sources highlighted the possibility of introducing “transitional arrangements” which could potentially reduce the 10-year wait for some existing migrants.

The Home Office has had 200,000 responses to its consultation on the reforms and is still considering how to apply the changes to those already in the UK.

But the Folkestone MP Tony Vaughan, who sent a letter signed by 100 colleagues to the home secretary expressing opposition to the changes, told the BBC that transitional arrangements would not be enough to overcome objections.

He said the MPs’ concerns were more “fundamental” and the government should not proceed with any of the rule changes to ILR.

Labour MPs have so far been expressing concerns about the changes privately.

One said that it was wrong to “renege on promises” by making people who “uprooted their lives to come here” to wait longer for permanent residency.

Another said their opposition was “non-negotiable” and the reforms needed to be “binned” rather than mitigated.

A former minister said the issue had come up in some communities in the Gorton and Denton by-election, which Labour lost last month.

A long-standing critic said “it is better to cringe and do a U-turn than do the wrong thing”.

There was support for some of the home secretary’s changes, such as new safe and legal routes, but the MPs were keen to see the details.

But the ILR changes provoked the most ire.

Multiple sources have told the BBC that they intend to invoke little-used parliamentary procedures to force a vote in the coming months.

The BBC understands there is likely to be a debate on the changes in the Lords, too.

But parliamentary votes would only be symbolic, and would not be binding on the government.

However, the MPs opposed to the ILR changes believe the mere prospect of a vote could still provide a valuable weapon.

As one of them explained, it would highlight divisions on a politically toxic issue for Labour unless ministers back down.