Delegates at the Liberal Democrats' annual conference in Liverpool voted to back marriage equality for gay and straight couples this morning.
The motion called to open up marriage and civil partnerships to straight and gay couples, allow religious celebrants to hold same-sex marriages and civil partnerships if they wish to do so, and to allow trans men and women the right to stay married or civilly partnered when they legally change their gender.
It cited Liberal Democrat leader and deputy prime minister Nick Clegg's comments to PinkNews.co.uk earlier this year.
Mr Clegg said in February: "I support gay marriage. Love is the same, straight or gay, so the civil institution should be the same too. All couples should be able to make that commitment to one another."
Speaking after the motion passed, Liberal Democrat MP Steve Gilbert said: “This policy underlines, once again, that equality is in the DNA of our party. Today, Liberal Democrat members showed that the party remains in the vanguard of the progressive movement and won’t settle until everyone enjoys equal status.
“Current legislation degrades same-sex couples to a second-tier partnership and leads to unnecessary pain and trouble for anyone wishing to change their legally recognised gender, forcing them to divorce or dissolve their civil partnership and enter into a different commitment.
"It is time that Britain ends the current unfair legal situation and regains its position as a country leading the fight for full LGBT equality.”
Speaking to PinkNews.co.uk, Mr Gilbert said the move would give "MPs and ministers a platform to argue within the coalition that it is time we caught up with other European countries".
He added: "I'm really pleased the party has reaffirmed its commitment to equality."
The move means that the party is expected to lobby for the legal change and now officially supports it.