Diane Abbott, the first female black MP, has become the first woman to enter the race for the Labour leadership.

Ms Abbott is the sixth candidate in the race to succeed Gordon Brown, following David Miliband, Ed Miliband, Ed Balls, Andy Burnham and John McDonnell.

Although she has spoken in favour of gay rights and been a judge in the Stonewall awards, she has missed more than half of the gay rights votes she could have attended since 1998.

Ms Abbott has never voted against gay rights measures, but was absent for some votes on gay couples adopting, civil partnerships and equalising the age of consent.

She missed all votes on repealing Section 28 in 2003 and scrapping the need for a father in fertility treatment in 2008.

Stonewall gave her a 79 per cent rating for her gay support.

In 2005, she was ranked among the MPs with the worst Commons attendance record.

The 56-year-old left-winger is well-known as a orator and political commentator, appearing weekly on the BBC political show This Week with Michael Portillo.

She announced her surprise candidacy this morning, overshadowing former health secretary Mr Burnham’s announcement.

Ms Abbott told Sky News she was confident of securing the 33 nominations needed and added: “I am attracting support not just from the Left but from women and other MPs that want to see a more diverse range of candidates.”

She is the only woman so far to stand for the leadership, as Harriet Harman and Yvette Cooper have ruled themselves out.

Mr Burnham, who has voted against lesbian fertility rights and abstained from votes on gay couples adopting, launched his bid this morning.

He wrote in the Daily Mirror: “We must become a new kind of party that involves and consults its members on a daily basis – truly a People’s Party – and reduces the influence of small elites at the top.

“Politics has changed. Our job is to reconnect Labour with people who want something different from it. We also must bring back those people who have lost faith with us. I believe I can reach them.”

The most gay-friendly of the six candidates is Mr McDonnell, who has voted in favour of every gay equality measure, including gay couples adopting and civil partnerships, since becoming an MP in 1997. However, he is unlikely to be able to raise the support he needs.

Nominations close next week but the lengthy candidacy process means a new leader will not be elected until September.