Ann Widdecombe is supporting the owners of a Belfast bakery who refused to make a cake featuring a pro-equal marriage message.
The County Antrim firm could face legal action from the Equality Commission.
It is assisting the customer whose order was refused and has written to the baking company on his behalf.
The cake was ordered for a civic event in Bangor Castle Town Hall, County Down, to mark International Day Against Homophobia and Transphobia.
Writing in her weekly column for The Express, former Conservative MP Ann Widdecombe said: “If the baker had refused merely to bake a cake because the customer was gay then that would indeed have been both unpleasant and illegal but the refusal was specific to the message requested for the cake.
“Surely it is an elementary feature of true democracy that nobody should be obliged by law to affirm that which he or she does not believe.”
She added: “In a free country the baker should be able to refuse to take part in what is effectively PR for gay marriage in the knowledge that any customers who do not like that decision are free to buy their morning loaf elsewhere.
“But then it is a long time since Britain and freedom were synonymous.”
Widdecombe, a staunch opponent of equal marriage, moved on to take a swipe at David Cameron in her article.
“Parliament was assured time and again that the introduction of gay marriage would not cause discrimination against those who believed it wrong. What price your assurances now, Mr Cameron?”
She then mentioned the case of a Christian woman who it’s claimed was prevented from becoming a foster parent due to her views on marriage rights for gay couples.
“In my postbag this week is a letter from someone who had reached the final stages for approval as a foster parent but was rejected because she would not affirm that a gay relationship was on a par with a marriage between a man and a woman.
“She was not immoderate about her views and said that of course she would be prepared to explore a young person’s sexuality sympathetically but that she did not regard all arrangements as equally valid. That’s an awful lot of potential fosterers eliminated.”
Northern Ireland is now the only part of the UK which has not passed a law to introduce same-sex marriage.
At PMQs on Wednesday, Ulster Unionist MP Gregory Campbell called for a “conscience clause”, allowing Ashers Baking Company to discriminate on the grounds of religious belief.
But Mr Cameron responded by saying tolerance and equality were “a very important part of being British”.