Plans to make migrants wait longer to get the right to live in the UK permanently should not apply to people already in the country, Labour MPs have said.

A letter to Home Secretary Shabana Mahmood, signed by 35 Labour MPs, along with 17 from other parties, 21 peers and 33 civil society organisations, says the proposals are "unfair towards migrant workers who have put down roots, contributed to their communities and built lives here".

Ministers want to double the time it takes for most migrants to qualify for permanent residence from five to 10 years.

Mahmood has defended the plans, saying the "unprecedented" number of people arriving in the UK demands an answer from the government.

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 government's proposed changes would extend the standard wait to qualify for settlement to 10 years.

Migrants will be able to shorten this period, for example if they are a high earner, while other groups would see a longer wait.

People who arrived on health and social care visas would face a 15-year wait, while those who relied on benefits for more than 12 months would have to wait 20 years.

The changes would not apply to people who have already obtained settlement but would cover people already living in the UK, including those who had been expecting to get permanent residence in the coming months.

The government has said migrants who come to the UK must contribute to earn their right to stay, arguing the scale of migration is placing pressure on local communities.

However, Labour MPs opposed to the plans have branded the retrospective approach "un-British" and "moving the goalposts".

The letter, which is also signed by Andrea Egan, the new head of the UK's biggest trade union Unison, says: "The British public believe in fair play: that if you work hard, follow the rules and contribute, that government should tread lightly on your life."

It adds: "The proposals to change settlement rules would pull the rug from under migrant workers, including in social care who provide dignity and comfort to our loved ones, often in difficult conditions and for low pay.

"The government must uphold its promises - we cannot simply change the rules halfway through an agreed process."

The letter warns there are already thousands of vacancies in social care and the proposals "risk pushing the sector closer to breaking point".

It calls on the government to "immediately rule out applying new immigration rules to migrant families already in the UK" and for a consultation process on the proposals, which closes at the end of Thursday, to be halted until a full impact assessment is published.

Labour MPs who have signed the letter are mostly on the left of the party and it was coordinated by Neil Duncan-Jordan, the MP for Poole who has called for the prime minister to resign over the Lord Mandelson scandal.

Other signatories include Alex Sobel, a leading member of the centre-left Mainstream group, former shadow chancellor John McDonnell and Rachael Maskell, who led a rebellion against benefit cuts last year.

Former Labour leader Jeremy Corbyn, Plaid Cymru Westminster Leader Liz Saville Roberts and all four Green Party MPs are also among those who signed the letter.

Concern over the plans among Labour MPs has been growing, with around 40 criticising the proposals in a recent debate in Parliament. (BBC)