Migrants already living in the UK will have to wait up to 10 years to be granted citizenship, under new plans.
Keir Starmer and Yvette Cooper confirmed the Home Office will double the length of time people have to live in the UK before they can apply for indefinite leave to remain.
Tory MPs warned it would not apply to "immigrants who are already here".
But Home Office sources have confirmed the changes will apply to migrants who have arrived in the UK in the last five years.
The measures were included in the Prime Minister's heavily criticised immigration reforms, which are designed to slash net migration from record highs and end abuse of the asylum system.
A document published in the coming weeks will make clear the government is preparing to apply the 10-year qualifying period to those who are already in the UK as well as to new visa applicants.
The move will be subject to a public consultation.
Tory MP Nick Timothy raised the alarm in a speech to Parliament.
He told MPs: "Ministers said that they would change indefinite leave to remain, but the White Paper proposal today is weak, and the Home Secretary admitted that it may not apply to immigrants who are already here.
"It is therefore no wonder that the Government refuse to support new clause 11, which would do the job for them.
"The visa crackdown on the nationalities blamed for asylum costs-Pakistanis, Nigerians and Sri Lankans, we were told-and the promise to kick out all foreign criminals were both headlines, but no credible policy on those issues was presented."
Labour believes its plans will reduce the number of people coming to the UK by 100,000.
Statisticians at the Office for National Statistics had prviously predicted net migration will settle at 340,000 per year from 2028.
But this could be higher, with current levels soaring at 728,000.
This is down from a record high of 906,000 in June 2023.
Measures in Labour's plan, dubbed "Restoring control over the immigration system", included:
- Increasing the threshold for the Skilled Worker Visa to graduate-level roles.
- Revoking visas for foreign thugs, shoplifters and sex offenders as the number of offenders eligible for deportation is expanded.
- Reforming citizenship rules by making migrants wait 10 years rather than five to apply for indefinite leave to remain, although workers who significantly contribute to society, such as nurses, doctors and engineers, could be fast-tracked.
- Requiring a higher standard of English across all immigration routes, including, for the first time, adult dependents required to display a basic understanding of the language.
- Closing the social care visa to foreign workers, amid fears it is being abused as a back door route into the UK.
Reform UK's newest MP Sarah Pochin meanwhile said Labour is sounding "more like Reform than Reform".
"Reform have got them on the run. They know what the electorate want to hear.
"They've seen the devastating impact of our policies on their results in these latest set of elections, and so now, yes, they're sounding more like Reform than Reform are," she told Times Radio.
But she said the immigration policies announced were "just a bit of bluster, a bit of waffle".
Downing Street has rejected the comparisons with Enoch Powell's "river of bloods speech", in which the then-senior Tory said white British people could find themselves "strangers in their own country" as a result of migration.
Sir Keir's official spokesman said on Tuesday that the Prime Minister stands by his words.
"The Prime Minister rejects those comparisons and absolutely stands behind the argument he was making that migrants make a massive contribution to our country, but migration needs to be controlled."
Mayor of London Sir Sadiq Khan led a Left-wing Labour backlash on Tuesday, refusing to support Sir Keir's language as others accused him of echoing Enoch Powell's "rivers of blood" speech.
Sir Sadiq said: "Well, look, the sort of language that I use is different to the sort of language used by others. That's not the sort of words that I would use.
"We've gone from a situation where lawful migration was 100,000, 200,000 to where it's 900,000, 700,000, more than 600,000, and I think we should have control over our borders, but I think you can be consistent in saying that and also recognising the massive contribution made by successive generations of migrants."
Pressed on how he felt about the Labour leader's comments, Sir Sadiq repeatedly dodged the question, insisting: "You know when you read the entire White Paper, the White Paper actually is about solutions to some of the challenges."
Labour MP Olivia Blake condemned Sir Keir's language, claiming it "could legitimise the same kind of far-right violence that we saw in the last year".
She told Times Radio: "I was very disappointed to hear him use such language because we know that language has consequences. I worry that this could legitimise the same kind of far-right violence that we saw in the last year. As politicians, we have a responsibility not to pour fuel on a fire by using language that causes division."
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