A human rights lawyer has said the ruling over a Belfast bakery which refused to make a cake celebrating gay marriage could force people with religious beliefs to break the law rather than adhere to their chosen doctrine, the Telegraph reports.

The cake, which featured Sesame Street characters Bert and Ernie with their arms around each other and a slogan supporting gay marriage, was ordered for International Day Against Homophobia.

Aiden O’Neill QC said there was a risk that the case taken by Gareth Lee and supported by the Equality Commission of Northern Ireland could undermine freedom of conscience.

And he compared it to the execution of Sir Thomas More after he refused to acknowledge Henry VIII as Head of the Church of England, saying that Commission’s case ignored human rights in its bid to eliminate discrimination – even if that means discriminating against people who hold religious beliefs.

The case has led the DUP in Northern Ireland to put forward a proposal which would give businesses an exclusion from discrimination law enabling them to turn down work should it go against their religious convictions. Supporters of the “conscience clause” say it is needed to protect freedom of beliefs but others say it just legalises discrimination, particularly against gay people.

“Their refusal to endorse this opinion – to protect their negative freedom of expression – has resulted in the State, in the form of the Equality Commission for Northern Ireland, funding court action against them which seeks to stigmatise as unlawful and render unactionable the defendants’ religious beliefs and political opinions,” Mr O’Neill wrote.

“If the approach of the Equality Commission for Northern Ireland … were correctly based in law (which I do not consider it to be) then on the basis that the law does not protect the fundamental right, within the commercial context of supplying services, to hold opinions nor guarantee any negative freedom of expression, there would be no defence to similar actions being taken against individuals or companies supplying services in any of the following scenarios which have been presented to me.”

The lawyer detailed several scenarios which could occur should the Commission win against the bakery including forcing a Muslim printer to take on a contract requiring him to print the cartoons of Mohammed or a lesbian t-shirt company being forced to make t-shirts saying gay people are an “abomination”.

His opinions were welcomed by Colin Hart, the director of the Christian Institute, who said: “The strength and clarity of the advice from Mr O’Neill, who has a national reputation for his human rights expertise, should set off the alarm bells in this Government quango.

“It spells out the very real dangers and far-reaching implications for freedom of speech.

“But the equality watchdog seems determined to force people to use their creative skills to promote a political cause they fundamentally disagree with.

“This family run bakers serve gay customers all the time but they didn’t want to promote gay marriage.”