Liberal Democrat Business Secretary Vince Cable has said he believes the current system of civil partnerships for gay couples is ‘fine’, but that it is ‘difficult’ to justify a ban on gay civil marriages and will support plans to lift it.

The former deputy leader of the party was replying to a letter from a constituent. His response was published in the print edition of the Daily Telegraph but has not appeared online.

Liberal Democrat leader and deputy prime minister Nick Clegg has confirmed that his MPs will be whipped to support the marriage legislation when it comes before Parliament.

He said in May: ”In the same way the civil partnerships legislation which was introduced under Labour was a whipped vote, I personally don’t think this is something which should be subject to a great free for all because we are not asking people to make a decision of conscience.”

In response to an enquiry from a constituent, Dr Cable wrote: “On the issue of same–sex marriage, my own personal view is that the status quo is fine, with same–sex couples being able to commit in a civil partnership.

“However, if there is a confrontation over the issue it is difficult to explain why a civil partnership cannot be called a civil marriage and if it comes to a vote I would vote in favour of same–sex civil marriage.”

The Coalition for Marriage, which is campaigning against the government’s proposals to allow gay couples to marry, claimed Dr Cable’s letter demonstrated a “sense of unease” that the measure would have “serious repercussions on ordinary people, schools, institutions like churches and charities that oppose the change”.

Dr Cable was replaced as deputy party leader by bisexual MP Simon Hughes when he was appointed business secretary.