Britain would breach international obligations if it failed to enforce legal recognition for same-sex unions in its Overseas Territories, a former Cayman Islands lawyer has said.

Leonardo Raznovich, joint vice-chairman of the International Bar Association’s LGBTI Law Committee, added that a Foreign Office commitment that ministers would work with the British Overseas Territories “so they can drive their own lasting legislative change” was not enough.

Mr Raznovich said: “Nothing short of independence will restrict the power of Parliament.

“The Foreign Office statement is not enough — there is a clear distinction that needs to be made between policy and international law.

“There is a clear dereliction of duty by the UK Government when it comes to international human rights, particularly as it relates to the LGBT community.

“They are responsible, and they can’t just say they will continue to ‘encourage and engage’ — that doesn’t work when there are international obligations in place that have been breached.”

Mr Raznovich added: “This is for the UK to tell the world — here is a list of obligations under the European Court of Human Rights. You are bound by it, you have to comply. You have five years to catch up.

“This is what I am trying to push Parliament to do.” He was speaking after the Foreign Office said it welcomed a Bermuda Supreme Court decision “in favour of same-sex marriage rights” — which is to be appealed by the Government.

A spokeswoman for the Foreign Office added: “Ministers will continue to encourage and engage with all of the Overseas Territories on these matters so they can drive their own lasting legislative change.”

The IBA’s Human Rights Institute wrote to David Burt, the Premier, in June and asked him to accept the court ruling that reinstated gay marriage, which had become legal last year, but was outlawed again by the Domestic Partnership Act months later.

The DPA removed full marriage rights for gay people last December and replaced them with civil union-type arrangements available to both gay and heterosexual couples.

The IBAHRI acted after Mr Raznovich’s committee highlighted “breaches of international law by the UK Government”.

The Human Rights Institute also wrote to Boris Johnson, then British Foreign Secretary, to condemn the UK Government’s failure to order John Rankin, the Governor, to refuse to give Royal Assent to the Domestic Partnership Act

Mr Raznovich, who won a legal challenge to be listed as a dependent on his same-sex partner’s work permit under Caymanian immigration law, said the UK should give its Overseas Territories a timeline to change their legislation.

The European Court of Human Rights has ruled in favour of legal recognition for same-sex unions, but has not backed full marriage rights for gay people.

Mr Raznovich trained as a lawyer in his homeland of Argentina and later qualified as a barrister in England and Wales.

He was a principal lecturer at Canterbury Christ Church University in the UK, as well as a law lecturer at the Bodden Law School in the Cayman Islands.

The Cayman Islands is also locked in controversy over same-sex marriage and the rights of gay people. Two women were last month granted leave to apply for a judicial review of a Cayman Islands government decision to refuse their application to marry.

A UK Foreign Affairs Committee has been set up to examine how the Foreign Office manages its responsibilities to “ensure the security and stability of the UK’s 14 OTs”, including “instances of divergence between the UK and some of the Overseas Territories on issues such as civil rights and financial transparency”.

A Bermuda government insider, who asked not to be identified, said there was growing pressure for the introduction of same-sex rights, but that it came mainly from Britain and the European Union.

The source said: “It is the obligations that the UK have at the moment with the ECHR and any removal from Brexit doesn’t remove that so it is more a pressure from Europe and the UK rather than an international pressure so far.

“Pressure is growing but I think that a lot of it is politicking because the UK has to make a decision not only on the decision of SSM, but also on the registration of beneficial owners.

“I believe the UK will engage and have more direct consultation diplomatically with Bermuda, but they will have to resolve the issue as to whether this is a domestic issue or an international issue under section 62 of the Constitution.”

A Government House spokeswoman said: “The Governor remains committed to upholding compliance with the Constitution and international obligations in accordance with his responsibilities.

“The decision of the Supreme Court in relation to the constitutionality of the Domestic Partnership Act is now the subject of an appeal and it would be inappropriate to comment further on the particular issues in that case.”

A spokeswoman for Mr Burt also said it would not be appropriate to discuss a case before the courts.