LONDON (AP) — A simmering dispute over Britain's treatment of people who came to the country as children decades ago has erupted just as the country prepares to host leaders from the 53-nation Commonwealth.

Britain had wanted to use this week's summit in London of the alliance of the U.K. and its former colonies to help Britain bolster trade and diplomatic ties around the world after it leaves the European Union next year. But trade topics are being overshadowed by anger over what some in the Commonwealth see as the U.K.'s shabby treatment of residents of Caribbean origin.

British Prime Minister Theresa May's office said Monday that she would meet with her Caribbean counterparts in London for the Commonwealth summit to discuss the situation of long-term U.K. residents who say they have been threatened with deportation to their countries of birth.

Members of the "Windrush generation" — named for the ship Empire Windrush, which brought the first big group of post-war Caribbean immigrants to Britain in 1948 — came from what were then British colonies or newly independent states and had an automatic right to settle in the U.K.

But some from that generation, now aging and long-times residents in Britain, say they have been denied medical treatment or threatened with deportation because they can't produce papers to prove it.

The British government has taken an increasingly tough line on immigration, which has increased dramatically over the last 10 or 15 years, largely as result of people moving to the U.K. from other EU countries. A desire to control immigration was a major factor for many who voted in 2016 for Britain to leave the bloc.

Critics say the British government has, by design or accident, taken a hostile attitude to the thousands of people who have made Britain their home.

Barbados High Commissioner Guy Hewitt told the BBC on Monday that he felt Britain was telling people from the Caribbean "you are no longer welcome."

Some 140 U.K. 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 Monday 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 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 the British 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, which says the choice of its next leader will be a decision for the group.