The following correction was printed in the Guardian's Corrections and clarifications column, Thursday 27 May 2010

The profile below of Diane Abbott mentioned some ongoing resentment at a past decision by the Labour MP and party leadership hopeful to send her son to a fee-paying school, "given her position on the left and her criticism of Tony Blair and Harriet Harman for making the same educational choices". In the latter two cases, the schools involved – London Oratory, and St Olave's grammar in Kent – were actually state-funded. Choice of the Oratory was criticised because the school had opted out of local authority control; choice of St Olave's was criticised because admission was selective.

'I'm just wondering what to ask you next," said a bewildered James Naughtie on the Today programme this morning. And that was worth a headline in itself. It is not often that the broadcaster, essayist, master of vocabulary meets a phenomenon that renders him inarticulate. But it was on Naughtie that Diane Abbott, Labour MP, journalist, television star, formerly the high priestess of New Labour's awkward squad, dropped her bombshell – first mooted in Thursday's Guardian – that she intends to contest the Labour leadership. Others listening from the Labour establishment will have been just as surprised as Naughtie; horrified even. Lucky for them that they didn't have to react in front of a mic.

And why was it so surprising? Well look at the contenders so far. Two Milibands, Ed Balls, Andy Burnham, John McDonnell. Five straight white men, all with a track record – or is that a charge sheet – of chasing high office in the past, the bad old days. Each is imbued with their own distinctive qualities, it is true. But one can look at the contestants and wonder, what about diversity?

So, at a stroke, Abbott's dramatic statement of intent changes the dynamic of Labour's competition for its highest office. Many would say the dynamic badly needed changing. But is Abbott the person to do it?

Definitely yes, says Simon Woolley, director of Operation Black Vote, who floated the idea of an Abbott candidacy on the Guardian's Comment is Free site on Wednesday. "Above all, Diane came into politics to tackle racial inequality," says Woolley. "She has a track record of speaking out and a track record of difficult battles. Think of the fight all those years ago against the Sus laws, the Stephen Lawrence issue. You get the odd curve ball from her and you think, where did that come from. But she is strong left and has a record in grassroots politics that makes us extremely proud of her."

Yes, says Hilary Wainwright, the socialist feminist writer and former editor of periodical Red Pepper. "She will stir things up and open things up. Things need stirring up. It was completely closed down under Blair and debate was frowned upon." It is not just about having a woman run, she says. "If Patricia Hewitt was running, I wouldn't be very confident. But Diane was never a Blair babe. I disagree with her on some things; PR and the importance of comprehensive education. But she was against the war and has independence of spirit."

Yes, says leftwing Labour MP Jeremy Corbyn, also a fan of John McDonnell. "There was an attempt to railroad the debate into a small number of candidates, but we need a wide range," he says. "Both are good colleagues, experienced, well informed. We need that kind of candidate."

Some would support her decision to run, even if they don't support Abbott herself, among them the writer Suzanne Moore, who ran against the Labour backbencher in her heartland Hackney North and Stoke Newington. "I am very glad she is standing because I am one of the people who complained that there is not enough diversity," Moore says.

"I don't think she is a fantastically good MP or would be a good leader of the Labour party. But I respect that fact that she has put her hat in the ring."

So she has friends, faithful and fair-weather, but given her profile and a track record, who can be surprised that she also has enemies? In the weeks to come, she may hear a great deal from them. "Diane sold her principles by sending her kids to private school and spending a lot of time on the box cosying up to Michael Portillo, making comments for the sake of projection on TV," one grumbled, anonymously, yesterday. "Is there much difference between her and George Galloway in the way they behave in the media? This may be more about Diane's ego than a serious bid."

Such comments are easily elicited around Westminster – predictions of failure voiced as much in hope as expectation. But then, Abbott says, hurrying from her airy office in Portcullis House to yet another rolling news interview, vitriol from the Labour establishment has long ceased to trouble her. "They have always seen me as troublesome because I am one of the few people who have managed to maintain a high profile which is not controlled by the party. I can't be bought. I have worked hard at my politics and I have always kept close to my base. There are a lot of people who don't agree with me about everything, but that's OK. They think that I am genuine and I speak my mind."

Certainly we have had long enough to get used to Diane Abbott, 56. She was elected to Westminster city council in 1982 as one of the first black female councillors. Her rise from municipal politics was speedy. In 1987 she was sent to parliament to become one of just four ethnic-minority MPs. Her first parliamentary speech concerned the inequities of Britain's immigration policies.

Of those four MPs, both Paul Boateng and Keith Vaz would ascend to high office, but Bernie Grant never benefited – perhaps he never wanted to – and Abbott's career has never before risen above the level of backbencher. But that is why, her supporters might argue, she has been so effective.

She has won widespread plaudits for her work investigating the underachievement of black children in London schools and highlighting the efforts of those who excel. She was a leader of the campaign to raise minority representation in politics through the "black sections" movement and she was one of the early campaigners for all-women shortlists. Her record on dealing with immigration cases in a multiracial constituency is impressive. She voted against the war and has taken a consistent stand against New Labour's erosion of civil liberties. Her contribution to the Commons debate on 42 days detention was described by Conservative MP David Davis as, "one of the finest speeches I have heard".

But undoubtedly she has baggage, and some of it may prove heavy for her if she collects the necessary signatures from colleagues and formally joins the race for the leadership. The heaviest will be her decision to send her son James to a private, fee-paying school, a position she herself described as "indefensible" and "intellectually incoherent", given her position on the left and her criticism of Tony Blair and Harriet Harman for making the same educational choices. She will have to deal with the continuing resentment from that decision. Like ash from the Icelandic volcano, it never quite goes away. But while acknowledging these inconsistencies, she remains unapologetic. "One of the things that marks me out from the rivals is that I brought up a child on my own for 18 years. I have had to take some difficult decisions. I have not done everything right, but it was absolutely the right thing for my son at the time. I don't regret that." It remains a handy, lumpy stick to beat her with, but she's sanguine. "If it hadn't been this, it would have been something else."

There has to be good reason to volunteer for the upheaval a leadership campaign would bring, but from the outside it is hard to see it. Despite the best efforts of Moore and the other wannabes in Hackney North, Abbott doubled her majority at this latest election. She's a backbencher, but not just a backbencher. She is also a celebrity. Her exposure on the late night political programme This Week, alongside Andrew Neil and all cosy with Michael Portillo on the pundits' sofa, was supposed to last for just four weeks. She has been doing the programme now for the last six years. "They do audience research and This Week has the highest audience appreciation of any political programme," she says proudly. "The next most favourite of those who liked our show was Midsomer Murders. I can relate to Middle England."

Everybody wants to. Why not settle for that? "I followed the Obama campaign and it seemed strange that when the US has a black president, we didn't even have a black candidate for our leadership. I looked at the front-runners, all male, all white, all former policy wonks, and it just seemed wrong. It is annoying that the Tories are now to the left of us on civil liberties. What are we going to do about Afghanistan. Where is the serious debate about the economy? Who is going to talk about the balance between cuts and tax? In Hackney, one person's public sector cut is another person's job. Many of them will be women, heads of households." The noises from the nascent campaign were not, she says, encouraging.

"One of the things that made me run was hearing candidate after candidate saying the immigration lost us the election. Rather than wringing our hands about the white working class and immigration, we need to deal with the underlying issues that make white and black people hostile to immigration; things like housing and job security. We need to be careful about scapegoating immigrants in a recession. We know where that leads."

It may all come to nothing. No 32 signatures, no leadership campaign. But amid the media frenzy that enveloped Abbott after her chat with James Naughtie, she was calm yesterday. Surprised at the level of attention, but knowing perhaps that after years on the sidelines, her candidature could do the party a vital service.

She has never sought to fly this close to the sun before, but she has always had respect for the notion of leadership. The photographs in her office show Nelson Mandela, Jesse Jackson, PJ Patterson, the former prime minister of Jamaica.

She might not be able to run, and if she did, it is barely conceivable that she could win. But that's not the point. The point would be the journey. "I looked at the situation and thought if not now, when? And if not me, who?"