Labour was plunged into a fresh civil war after Downing Street refused to back Shabana Mahmood's migrant crackdown following Angela Rayner's bombshell attack.

The former Deputy Prime Minister condemned the Home Secretary's plans to extend the settlement time for migrants who have already lived in the UK from five years to up to 20 years.

Ms Rayner said it is “un-British” to move “the goalposts” if foreign nationals have “obeyed the law and paid their taxes”.

Ms Mahmood had sought to convince MPs her plans were fair and necessary during a flagship speech this month, warning that failing to secure Britain's borders could lead to "ethno-nationalism".

More than 100 Labour MPs have written to Ms Mahmood warning that retrospectively changing the rules is unfair.

Ms Rayner said on Tuesday night: “Many people came here to Britain – on the understanding that if they worked in the sectors where we needed them, obeyed the law and paid their taxes, they could stay.

“If we suddenly change that, it pulls the rug from under those who have planned their lives and commitments and are contributing to our economy and to our society.

“That would be not just bad policy but a breach of trust. The people already in the system – who made a huge investment – now fear for their future, they do not have stability and do not know what will happen.

“We cannot talk about earning a settlement if we keep moving the goalposts, because moving the goalposts undermines our sense of fair play. It’s un-British.”

And Downing Street refused to commit to the reforms on Wednesday, stating it is “considering responses to Home Office consultation”.

The Prime Minister’s political spokesman said: “We’re a proud, tolerant, generous country.

“Labour’s always been the party that celebrates the contribution migrant communities have made to our national story.

“In the four years before the election we saw record levels of immigration. In the manifesto we promised to deliver a fair and properly managed immigration system.

“We are considering responses to the Home Office consultation and will respond in line with our principles and values.”

Under Labour’s plans, migrants will be told to wait at least 10 years before they can apply for settlement rights.

Foreign nationals who arrived in the so-called ‘Boris Wave’ face a 10 to 15-year wait to apply for indefinite leave to remain amid fears over an influx of low-skilled workers, particularly on the abused Health and Social Care Visa in the early part of this decade.

And migrants could be barred from claiming benefits unless they become British citizens.

Ms Mahmood said those relying on handouts must wait 20 to 30 years to receive indefinite leave to remain.

Arrivals applying for indefinite leave to remain after 10 years must have no criminal record, speak English to A-level standards and have no debt, under Labour’s new proposals.

Ms Mahmood had told the IPPR think-tank: “There is no denying that we meet at a difficult time for my party. It is a time when who we are and what we stand for is contested, sometimes bitterly, and nowhere is that contest more keenly felt than in the politics of migration.

“I have, of late, been offered wise counsel on this topic from certain quarters. I have been told that we must, quite simply, be more Labour. Well, you know what? I happen to agree we should be more Labour.

“Of course, we should be more Labour. The real question is, what does more Labour mean, because, in my view, more Labour doesn’t mean more Green, just like more Labour doesn’t mean more Reform.”

This is a breaking story. More to follow.