The British government on Monday apologised to Caribbean citizens who moved to Britain in the 1950s and 1960s and have been threatened with deportation, agreeing to meet 12 leaders of countries affected after initially turning them down.
Prime Minister Theresa May's meeting on Tuesday will come ahead of a summit of Commonwealth leaders this week, after more than 140 British MPs demanded her government stop treating members of the Windrush generation as illegal migrants.
"There is absolutely no question about their right to remain and I am very sorry for any confusion or anxiety felt," interior minister Amber Rudd told parliament during an emergency debate.
After the arrival of the first group of West Indian immigrants on the ship Empire Windrush in 1948, many more followed to help rebuild Britain in the wake of World War II.
They were given indefinite leave to remain, a situation which changed with a 1971 law -- but many who failed to get their papers in order are now being treated as undocumented or illegal migrants.
An online petition to parliament, calling for an "amnesty" for the Windrush generation, had almost 150,000 signatures on Monday.
Also facing fury from opposition lawmakers, who condemned a "national shame", Rudd announced a new taskforce to help those affected to regularise their immigration status swiftly and for free.
Pressed over the years-long clampdown on illegal immigration by the Conservative-led government, she also admitted that her department could "sometimes lose sight of the individual".
However, she said she did not believe anyone had actually been deported, although there have been media reports of people who were only saved by the last-minute intervention of lawyers.
The row has been brewing for some months but has erupted just as leaders of the 53 Commonwealth countries gather in London for their biennial heads of government meeting.
"When the Commonwealth heads of government are gathered in London, what a disgrace it is that this government has treated Commonwealth migrants in this way," Labour lawmaker Diane Abbott said.
Guy Hewitt, the London-born High Commissioner to Barbados, told BBC radio that he felt "the country of my birth is saying to people of my region you are no longer welcome on my shores".
"Because they came from British colonies which were not independent they felt they were British subjects, they felt there was no need for them to recognise their status," he said.
"And now, 40, 50 years on they are being told by the Home Office that they are illegal immigrants. They are being shut out of the system, some of them detained, others have been deported."
Opposition Labour lawmaker David Lammy, whose parents were from Guyana, organised a letter of cross-party MPs against what he said was a "grotesque, immoral and inhumane" situation.
The letter highlights how uncertainty surrounding people's immigration status has affected their right to work, to rent homes, to receive pensions or even access healthcare.
Lammy told MPs it was an issue "of national shame".
Earlier, the prime minister's spokesman said May "deeply values the contribution made by these and all Commonwealth citizens who have made a life in the UK".
"If there have been problems which people have been put through, that clearly would be a matter of regret," he added.
Commonwealth Secretary-General Patricia Scotland, who herself moved to Britain from Dominica when she was two years old, said the issue was one for individual countries to resolve with London.
She said it would be a "very challenging" week in general, adding: "Some of the internal issues have to remain just that, whatever your own personal views."