Liberal Democrat peer Shirley Williams, who previously called the same-sex marriage debate a “conflict between equality and liberty,” has defended her position after being challenged by an openly gay Church of Scotland minister.

Scott Rennie, minister of Queen’s Cross Church in Aberdeen, questioned the Privy Council member during the Lib Dem conference in Glasgow.

He asked: “How can Liberal Democrats who are part of the state justify voting against legislation which will end discrimination to one group of people?”

Baroness Williams said she had a good record when it came to voting for equality.

She said: “It is an issue of conscience. I do regard Christian marriage as a sacrament, and as a sacrament it is quite clear that it says it’s a marriage between a man and a woman.”

Her position does not mean people should be discriminated against, she argued.

She added: “I’m not going to apologise. I know who I am. I’m a Liberal Democrat, I’m a believer in equality. I believe in the sacrament of marriage which is distinct in my view from any civic legislation.”

The Scottish Parliament is currently observing the Marriage and Civil Partnership (Scotland) Bill, which aims to legalise same-sex marriage.

England and Wales passed the Marriage (Same Sex Couples) Act earlier this year, which received royal assent in June.

Previously, Williams spoke in favour of an amendment to allow civil registrars to opt out of providing same-sex marriages.

She also said that, as well as biological differences, men and women approach relationships differently – making opposite-sex couples the most “stable” parents.

She said: “Equality is not the same as sameness”.

From 2001–2004, Baroness Williams served as Leader of the Liberal Democrats in the House of Lords.