Gambia's decision to withdraw from the Commonwealth is something to "very much regret", the Foreign Office has said.
The African nation announced its departure, saying it will "never be a member of any neo-colonial institution".
It was not immediately clear what triggered the decision to leave the association of 54 countries largely made up of former British colonies, which was announced in a statement yesterday.
Though a popular destination for British tourists, The Gambia has been criticised in the past by the UK for human rights abuses, including when it executed nine death-row inmates by firing squad in August last year.
Rights groups such as Amnesty International have also criticised the government of president Yahya Jammeh for cracking down on dissent and targeting political opponents and sexual minorities for arrest and detention, among other alleged abuses.
A Foreign Office spokesman said: " Decisions on Commonwealth membership are a matter for each member government. We would very much regret Gambia, or any other country, deciding to leave the Commonwealth."
Bakary Dabo, former vice president of Gambia and chairman of the country's campaign for democratic change, said the Gambian people are generally "very happy" to be part of the Commonwealth.
He said Gambian authorities had recently been seeking attention and "picking up war against poorly specified enemies called 'western powers'".
He told BBC Radio 4's Today programme: "This has been building up over the past few years and accelerated, especially as the last week he (Mr Jammeh) was at the UN General Assembly and used his time located to him to go into some long rambling about the 'western powers' and their supposed hegemonic plans around the world."
Last month Mr Jammeh told the United Nations General Assembly homosexuality was one of the three ''biggest threats to human existence''.
He has also drawn international criticism for claiming he can cure Aids with a herbal body rub and bananas.
He took power in the tiny West African country after a 1994 coup.
The Queen takes a keen interest in the Commonwealth and is likely to be following developments closely.
The monarch is head of the organisation known as the Family of Nations but will be represented at next month's meeting of Commonwealth leaders in Sri Lanka by the Prince of Wales following a review of her long-haul travel.
Buckingham Palace declined to comment on Gambia's announcement.