Labour politician Oona King has become the latest to film a video for the Out4Marriage campaign, saying her support is inspired by the fact that her parents’ mixed-race marriage would have been illegal in some parts of the US at the time they wed.

The second black female MP to be elected in the UK, she become Channel 4′s Chief Diversity Officer after being defeated by George Galloway in a 2005 election for Bethnal Green and Bow.

In 2011, she resigned that post to become Baroness King of Bow and sit on the Labour benches at the House of Lords.

Baroness King said in her video: “When my black father married my white mother it was illegal for them to get married in several American states and today we have the same thing for gay people.

“It’s outrageous that they do not have equal rights in terms of marriage, that’s why I’m coming Out4Marriage, I hope you do too.”

Baroness King told the Evening Standard her parents had a “terrible struggle because it was so completely unacceptable at the time for a white girl of my mum’s background to marry a black man”.

“My mum’s family were devastated, just as some parents feel today when they find their kids are gay and want to get married to someone of the same sex.”

Supporters of the Out4Marriage campaign so far include the Home Secretary Theresa May, Shadow Chancellor Ed Balls, Shadow Home Secretary Yvonne CooperSir Richard Branson, the Virgin founder; The Saturdays girl groupJack Straw, the former Foreign Secretary; David Walliams, the  Britain’s Got Talent judge; Caroline Lucas, the leader of the Green party; Lynne Featherstone, the Lib Dem Equalities Minister; Peter Tatchell, the  gay rights campaigner; Lord (Chris) Smith), the Advertising Standards Authority chairman and Rabbi Ariel Friedlander.