The UN judge Patrick Robinson concluded last year that the UK owed more than £18tn in reparations for its historical involvement in slavery in 14 countries.

Successive UK governments have resisted calls for reparations. Downing Street sought to shut down the discussion before the Commonwealth summit this week by saying that reparations were "not on the agenda". The government has also ruled out making a formal apology this week.

As the meeting in Samoa approaches, the Commonwealth, which was created from the ashes of the British empire, faces bigger questions about its usefulness as an association.

Summit attendance by heads of government has declined. The Indian prime minister, Narendra Modi, and the South African president, Cyril Ramaphosa, are set to snub this week's meeting in favour of the BRICS summit in Russia.