Ahead of today's statement by equalities minister Maria Miller on gay marriage, there has been some confusion over Labour's position. The party previously indicated that it would impose  a three-line whip on its MPs (in favour of the bill), but now appears likely to offer a free vote. However, as one MP explained to me, there's been no U-turn. "The three-line whip only applied to civil ceremonies. Now the government has agreed to allow gay marriages in religious buildings, we will hold a free vote."
Although less numerous than those in the Conservatives, there are some in Miliband's party who are hostile towards gay marriage. Roger Godsiff, the MP for Birmingham Hall Green, has said he will oppose any law "redefining the current definition of marriage", while his parliamentary colleague Austin Mitchell tweeted  yesterday: "Gay marriage is neither urgent nor important.It's also a moral issue therefore a free vote on which basis it won't pass". Three other Labour MPs, Jim Dobbin, Joe Benton and Mary Glindon, have signed the Coalition For Marriage petition  against the proposal.
The Lib Dems have yet to say whether their MPs will be whipped in favour of gay marriage, but it's worth noting that Nick Clegg has previously criticised David Cameron's decision to offer Conservative MPs a free vote. He told  The Andrew Marr Show in May: "My view is that in the same way that the civil partnerships legislation that was introduced under Labour was a whipped vote, I personally don’t think this is something that should be subject to a great free-for-all because we’re not asking people to make a decision of conscience about religion."
Update: The Coalition for Equal Marriage has pointed me towards three other Labour MPs who oppose  gay marriage: Brian Donohoe, Paul Murphy, and Stephen Pound.