LGBT campaigners have called on Britain to urge leaders of Commonwealth countries to make same sex relations legal across the network of 53 mostly former British colonies.
As the week-long Commonwealth Heads of Government Meeting (CHOGM) got underway on Monday, they launched a petition calling for Britain to apologise for colonial era homophobic laws still used in 37 of the 53 member nations.
In nine states, it is punishable by life imprisonment.
Matt Beard, Executive Director of campaign group All Out, said despite a Commonwealth commitment to create a "better future for all citizens", there was no plan to discuss lesbian, gay, bisexual and transgender decriminalisation at the summit.
"If the leaders gathering in London and Windsor want the Commonwealth to be recognised as a credible 21st Century global body, they must include an open and frank discussion of LGBT decriminalisation on their agenda," Beard said in a statement.
Britain's Interior ministry, or Home Office, was not immediately available to comment on the call for Britain to apologise.
The fact homosexuality is illegal across 70 per cent of the Commonwealth hit headlines last week when British diver Tom Daley used the spotlight after his fourth Commonwealth Games gold medal win to call for more countries in the group to act.
"I feel extremely lucky to compete openly as who I am and not worry about ramifications. But for lots of people living in those countries it is not the case," Daley, who married US Director Dustin Lance Black last year, told BBC Breakfast.
A Commonwealth Secretariat spokesman said there were more LGBT events this year than at the last CHOGM in 2015 including a roundtable on LGBT rights and reception to brief lawmakers on economic developments favouring decriminalisation.
He added that the Commonwealth Secretariat worked closely with parliaments to encourage them "to become parliamentary human rights champions for equality".
But activists angered by the Commonwealth's failure to put LGBT decriminalisation on the agenda said they were planning to picket the Commonwealth Secretariat's offices on Thursday.
Qasim Iqbal, an activist with Pakistani LGBT organisation Naz Male Health Alliance, said Britain should apologise for homophobic laws left in its wake, with same sex sexual activity still punishable in Pakistan by up to 10 years in jail.
"The UK has a responsibility to undo the damage that they caused. They need to not only apologise but also pressure countries to decriminalise by putting conditions on any aide they give," Iqbal told the Thomson Reuters Foundation.
But Frank Mugisha, an LGBT activist in Uganda where same-sex sexual activity can be punished with life imprisonment, said it was important Britain was not seen as "giving a lecture" as that could further alienate LGBT communities.
Seychelles activist Fabianna Bonne echoed similar concerns, urging Britain to support activists and advocates with "quiet diplomacy" to help push discussions forward.