Kingston and Surbiton's MP Edward Davey will back gay marriage in this afternoon's House of Commons vote.
He said: "I think if a couple wish to declare their love and commitment to each other, I do not think the state should get in the way.
"I think marriage is a fantastic institution, I am very happily married, and I think this bill will strengthen marriage.
"I am absolutely determined that we defend freedom of speech but equally it is right that couples who want to get married should.
"In a diverse society we should respect people’s diversity and rights, and this is part of that."
The majority of Liberal Democrats are expected to vote for the proposals, standing by their slogan ‘Taking pride in delivering equal marriage’.
If passed, the new marriage bill will allow people of the same sex to get married, unless they belong to a religion that opts out.
Certain Christian denominations, such as the Church of England, and Church in Wales, will not be allowed to perform gay marriages.
The bill amends the 1955 marriage act, inserting a definition of marriage defined as ‘the union of 2 people, regardless of their sex, sexual orientation, or gender identity’.
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