Britain is hosting leaders from the 53-nation Commonwealth in London this week as it seeks to bolster trade ties around the world after Brexit. But the gathering of the alliance of the U.K. and its former colonies is being overshadowed by a row over people who moved to Britain from Commonwealth countries as children decades ago.

Some members of the "Windrush generation" — named for the ship Empire Windrush, which brought hundreds of Caribbean immigrants to Britain in 1948 — say they have been threatened with deportation despite living in the U.K. for most of their lives.

They came from what were then British colonies or newly independent states, and had an automatic right to settle in the U.K. But some say they have been denied medical treatment or threatened with deportation because they can't produce papers to prove it.

Barbados High Commissioner Guy Hewitt said the British government has refused a request to meet Caribbean leaders on the issue during this week's Commonwealth summit.

Hewitt told the BBC yesterday that he felt Britain was telling people from the Caribbean "you are no longer welcome."

Some 140 lawmakers have signed a letter urging the government to find an "immediate and effective" response to concerns from Commonwealth-born residents over their immigration status.

International Development Secretary Penny Mordaunt said yesterday that the government must "do a better job" to put people's minds at ease.

"People should not be concerned about this — they have the right to stay and we should be reassuring them of that," Mordaunt told the BBC.

The dispute is an unwelcome distraction for Britain, which hopes to use the biennial Commonwealth summit to bolster its bid for free trade deals around the world after the U.K. leaves the European Union next year. The Commonwealth links 2.4 billion people on five continents, in countries from vast India and wealthy Australia to small island states like Tonga and Vanuatu. It espouses good governance, economic growth and human rights, but is seen by some as a vestige of empire with an uncertain mission in the 21st century.

Queen Elizabeth II, who will formally open the Commonwealth Heads of Government meeting at Buckingham Palace on Thursday, has done much to unite the group. She has visited nearly every Commonwealth nation, often multiple times, over her 66-year reign.

The 91-year-old has given up long-distance travel, so this is likely to be the last Commonwealth summit she presides over. Heir to the throne Prince Charles will not automatically succeed her as head of the Commonwealth. The Commonwealth says that will be a decision for the group.