Yesterday’s news of Lord Carey’s support for a new “Coalition for Marriage” set up to oppose same-sex marriage is a reminder that the battle for LGBT equality is not over.

Take a look at the list of supporters of this so-called “Coalition for Marriage”. It reveals a who’s who of figures opposed to almost every progressive measure brought forward to deliver equal rights for gays and lesbians in Britain. Their main concern is not being for marriage but against gay rights. The issue of marriage is just the latest front on which they’ve chosen to fight their regressive battle against equality.

Lord Carey thinks that legalising same-sex marriage would change the institution “beyond all recognition”. I think it would change it for the better.

One of my proudest achievements as London mayor was the introduction of Britain’s first partnerships register for gay and lesbian couples. Following this, the Labour government brought in civil partnerships across the UK. This was a bold and very welcome move. But I have always believed that our goal should be full and equal marriage rights for gay and lesbian couples.

Some people say that because civil partnerships confer almost all the same legal benefits to same-sex couples as marriage does that there is no need to introduce full gay marriage. But marriage is not just about legal rights – it’s also about social status. Granting gay couples the right to marry on the same basis as straight couples sends a clear signal that we do not regard them as second class citizens.

It’s not as if Britain would be alone in the world if we were to legalise gay marriage. Other countries have already recognised that restricting marriage to heterosexual couples is inherently discriminatory. Argentina, Belgium, Canada, Iceland, The Netherlands, Norway, Portugal, South Africa, Spain and Sweden have all legalised full gay marriage. So have parts of the Untied States, Brazil and Mexico. And guess what? Civilization has not collapsed as the anti-gay marriage lobby would have us believe it would.

Britain already has some of the world’s most progressive laws on gay rights. By legalising gay marriage, we would cement out reputation as a beacon of gay rights in the world.