Supporters of same-sex marriage would have a “good chance” of victory if their case was heard in the European Court of Human Rights, a constitutional expert said.

Nicola Barker, a professor of law at the University of Liverpool in England, highlighted legal arguments that could be used in Strasbourg, which were not available to teams at the Privy Council in London.

Her comments came after a majority ruling by judges at Bermuda’s highest court of appeal found that legislation confining marriage to between a man and a woman was not unconstitutional.

Professor Barker said: “Now the case has gone through the domestic courts, it is possible to take the case to the Strasbourg Court and make the European Convention arguments based on right to marry, right to family life, and prohibition of discrimination on the basis of sexual orientation – articles 12, 8 and 14.

“It wasn’t possible to make these arguments in the Bermuda courts or Privy Council because those convention rights are not included in the Bermuda Constitution, so instead the arguments were necessarily limited to the provisions of the Bermuda Constitution and Article 9 of the European Convention on Human Rights, the right to freedom of religion.”

She added: “In my opinion, a case heard in Strasbourg based on articles 8, 12 and 14 convention arguments would have a very good chance of success for LGBT people who want to get married.

“There seems to be an assumption that the convention does not recognise a right to same-sex marriage but those decisions are several years old now.

“As same-sex marriage becomes more and more the norm in Council of Europe states, the margin of appreciation – which is the level of discretion states have – narrows and sometimes it can narrow quite quickly, so it’s not necessarily out of question that the Strasbourg Court’s view on whether same-sex marriage is required might have changed in recent years since the last case.

“This is especially the case given that they will be influenced by the Inter-American Court of Human Rights’ view that their convention, which has similar wording to the ECHR, now includes same-sex marriage within the right to marry.”

Four out of five judges on a Privy Council panel agreed with the Attorney-General for Bermuda and ruled that the Domestic Partnership Act did not violate the Constitution.

Lord Sales reached a different conclusion to the majority and said that he would have dismissed the appeal based on a freedom of conscience argument put forward by lawyers for the respondents, who were Roderick Ferguson and others.

Professor Barker's research includes the history of the Constitution and the relationship between Bermuda and the UK in relation to LGBT rights and the protection of human rights in general.

She explained that the island’s circumstances were different to earlier claims heard at the European Court of Human Rights because same-sex marriage was allowed when the DPA was enacted.

Professor Barker added: “The court has said previously that Article 12 may not necessarily in all circumstances be restricted to heterosexual marriage and the Bermuda case would be different to the previous cases because at the time of the DPA, same-sex marriage was included within national laws governing marriage.

“So I think there is a strong argument to begin with that in relation to Bermuda, same-sex marriage is – or at least was at the time the DPA was enacted – included in the definition of marriage under Article 12 and therefore the DPA is a violation of Article 12.”

The academic said another argument could be made that revoking the right to marry for same-sex couples and not opposite-sex couples was “discrimination on the basis of sexual orientation under Article 14” of the ECHR.

She added that in that instance it would fall to the UK Government as the “defendant state” to show that the revocation was not discriminatory.

Professor Barker added: “In order to do this, they would need to demonstrate that it is a proportionate response to a legitimate aim.

“I think that would be an uphill task because it is well-established in the convention case law that differences in treatment based on sexual orientation require ‘particularly serious reasons’ by way of justification.

“Had the DPA been passed before same-sex marriage was established under Bermuda law, it may have been possible to justify it as a political compromise between different points of view.

“Now that same-sex marriages have been recognised for four years, the UK will struggle to explain the revocation of a fundamental right in a way that does not suggest it is based on discriminatory attitudes towards same-sex relationships.”

The Bermuda Tourism Authority was asked this week if the organisation was concerned that the Privy Council decision would damage the island’s reputation internationally and whether efforts would be made to show people overseas that the island can be welcoming to members of the LGBTQ community and their allies.

Charles H Jeffers II, the BTA chief executive officer, said: “Bermuda’s tourism industry has a long history of welcoming all travellers, including those of the LGBTQ+ community.

“The Bermuda Tourism Authority and our industry partners are committed to inclusiveness and receiving all visitors with open arms.

“Tourism is such a vital part of our Bermudian existence and we encourage the exchange of new ideas and cross-cultural understanding that visitors bring to our shores.

“Bermuda will continue to welcome all travellers with the warm hospitality our island is known for.”

Carnival Cruise Line, one of the “generous corporate allies” hailed by LGBTQ rights charity OutBermuda for enabling the group to present its arguments as a respondent in the case, said in 2018 it backed marriage equality.

A spokesman for Carnival Corporation said this week: “It has been an honour to work with OutBermuda on their never-ending journey to protect human rights and support equality.”

Wayne Furbert, the Minister for the Cabinet Office, who introduced a Private Member’s Bill to remove same-sex marriage from the Human Rights Act when he was an opposition MP in March 2016, declined to comment on the Privy Council judgment this week.

The Bill was passed by the House of Assembly but rejected by the Senate in July 2016.

Lieutenant-Colonel David Burch, the Minister of Public Works, was asked about the ruling on Wednesday.

He said: “I’m a member of the Government that took the case to the Privy Council and so I’m pleased with the outcome, as the proponents of same-sex marriage would have been had they won.”