A leading American LGBT rights advocate was the guest of honour at a private lunch at Downing St today.

Sarah Brown, the wife of the Prime Minister, hosted the event for David Mixner, a veteran American civil rights campaigner, author and political strategist.

It is thought to be the first time a gay activist has been honoured in this way at No 10.

Mrs Brown invited many prominent gay and lesbian Labour politicians to the lunch.

Chief Whip Nick Brown, Health minister Ben Bradshaw, Treasury minister Angela Eagle, Deputy Leader of the Commons Nick Bryant, MEP Michael Cashman and Ray Collins, the general secretary of the Labour party, were all there.

Gay basketball star John Amaechi was also among the 20 guests.

Mr Mixner, a former Clinton strategist, is known to the Browns and was a founding member of the Municipal Elections Committee of Los Angeles (MECLA), America’s first gay and lesbian Political Action Committee.

He is speaking at the Oxford Union later this week, and the lunch was “an interesting opportunity” to hear his thoughts on a range of subjects, a Downing St spokesperson said.

Mr Mixner was upbeat about LGBT rights in the UK and praised the progress that has been made in the past decade.

He also warned against taking those rights for granted.

He is a leading opponent of Proposition 8, a statewide ballot measure in California that seeks to impose a ban on same-sex marriage.

Mr Mixner, 62, became involved in Democratic politics in 1960 and made his name protesting against the Vietman War.

He came out in 1976 to fight a California ballot that would have made it illegal for gays and lesbians to be school teachers.

“No straight political consultant would touch it,” Mr Mixner recalled in 2004.

“I had a lot of political experience at that point.

“And they kept coming to me and asking me to run it. I was still in the closet, and I knew that if I ran it, I’d have to come out.

“But I also felt that if I didn’t do it, I could never live with myself.”

Mr Mixner raised money for President Clinton’s first campaign and worked on his transition team, but fell out with him after the ban on gays in the military was retained in 1993.

He was later arrested at a protest outside the White House.

Mr Mixner also fought for the rights of HIV positive people from the start of the epidemic. In 1985 he helped defeat Proposition 64, a California ballot initiative that would have quarantined people with AIDS.

In 2001 he published Brave Journeys: Profiles in Gay and Lesbian Courage. The Prime Minister published his own book, Courage: Eight Portraits, last year.

In an interview with Metro Weekly in 2004 he said:

“I know the most important act of my life was coming out, no question about it. It redefined my life. And it enabled me to operate as a free man.

“It enabled me to no longer live in shame and fear of judgement. It removed an enormous fear from my life of blackmail of destruction.

It made me part of one of the most magnificent tribes I’ve ever known in my generation. Extraordinary people who took care of their sick and dying and still staffed the barricades, fighting for liberty.

“I’ve never seen anything like it in my life. I’ve been involved in every kind of movement you can imagine, and this is one of the most magnificent stories around.

“One of the most magnificent tribes. I’ve seen courage like I have never seen courage in my life.”

Ben Summerskill, chief executive of gay equality organisation Stonewall, was at today’s lunch.

“It is fantastic that Sarah Brown has recognised that gay people, like eveyone else, have a place at the top table,” he told PinkNews.co.uk.

“It is another small historic step forward.”

In July her husband, Prime Minister Gordon Brown, met with members of Stonewall at Downing St to mark  Pride London, which was being held that day.

The meeting was attended by Stonewall co-founder Sir Ian McKellen.

Gordon Brown discussed a range of issues, including the new EU discrimination directive, the new Equality Bill and the work that Stonewall does through its Education for All programme tackling homophobic bullying in Britain’s schools.