'If you ever see me dancing on TV," Oona King wrote in her diaries, published after the former Labour MP for Bethnal Green and Bow lost her seat in the 2005 general election's bloodiest battle, "I can only apologise in advance." In that first year out of work, she turned down offers to appear on I'm a Celebrity ... Get Me Out of Here and host her own chat show. The only reality TV programme she "secretly yearned to do," she writes, was Dancing On Ice. Her long-suffering husband joked he would divorce her if she did it. Everyone else said it would "irrevocably ruin" her career.

Several years on, King, now 45, is about to take to the ice for the ITV show in which celebrities learn to skate and are voted off if they fail to shine. In a lineup that includes Pamela Anderson and Keith Chegwin, King seems like an odd choice. She had a high profile as one of the youngest MPs elected in the 1997 Labour landslide, but became better known for voting for the Iraq war, which led to one of the defining moments of the 2005 general election when she lost her seat to George Galloway, who campaigned on an antiwar ticket. Still, King doesn't seem publicity hungry in the way other politicians who do reality TV seem to be. This is the politician who set up the all-party parliamentary group on genocide prevention, and had a wonkish interest in housing and employment rights. When she campaigned for Labour's nomination for London mayor in 2010 (she lost to Ken Livingstone), she raised worthy subjects such as problems with the care system. She must be the only member of the House of Lords, where she sits on the Labour benches, to be getting so familiar with a spangly costume. Why on earth is she doing it?

"In the end, I couldn't resist," she says with a wide smile. Ice skating was always a passion, she says – as a child, the Winter Olympics was the one thing her mum would let her stay up late to watch, and she remembers, in 1997, competing to become a Labour candidate, "and I finish my speech [at the hustings] and I know I've done well, and the image that comes into my head is of an ice skater landing a near-perfect triple salchow. Ice skating has always been a symbol in my mind for executing something well." A loud laugh. "That no longer holds true now I have tried to skate."

And her career? These days King – or Baroness King of Bow as she is known in the Lords – doesn't seem too concerned about how going on a reality show might be perceived. "If I had done it at the time I left parliament, it would have defined me. People wait to see what you do next, and I didn't want the answer to be just ice skating, or eating a kangaroo's ear in the jungle. Now I'm far more relaxed."

Nadine Dorries was suspended from the Conservative party for appearing in I'm a Celebrity last year; King got a jokey text from Ed Miliband asking her to report to the office when her name was announced. "It would, in my view, be inappropriate for a serving politician to give up their parliamentary work to be [on a TV show] but that is not the case with me," she says. "I do an hour and a half training three mornings a week. I haven't missed a single parliamentary session." Dorries argued that by appearing on TV she was reaching people outside the Westminster bubble. King smiles. "I think George Galloway made that argument as well [he did Big Brother in 2006]. It doesn't really hold up. I'm certainly not going on to an ice rink to discuss my political views."

But it is about raising one's profile, isn't it? "That isn't the reason I'm doing it. I'm doing it because I love ice skating. There must be something you love that you've never had the chance to do, and if it was dangled in front of you for long enough you would eventually crack." She laughs. "That's how it is."

We sit in a quiet corner of a pub near King's home in Tower Hamlets. After the hostility she faced in the most personal of election campaigns – tyres slashed, colleagues abused and rumours spread that the Jewish MP was using her salary to help fund attacks on Palestinian children – many predicted she would leave this east London constituency and try for a seat elsewhere, but King remains committed to the area.

She knew, since the age of four, that she wanted to be an MP. Her father, Preston King, an African-American who was active in the civil rights movement, and her English mother, Hazel, a teacher from an Orthodox Jewish family, separated when King was small. At Haverstock comprehensive in north London she knew David and Ed Miliband ("I read about it being Labour's Eton," she says, "and it makes me laugh. I suppose when you get your head flushed down the toilet it could be similar in that respect, but not many others"). She later worked with Ed Miliband during her time at the policy unit. Would she describe them as friends? "When people get to the top of politics you see them less and less, so I wouldn't want to stretch the term," she says, before going on for several minutes about how brilliant she thinks Ed is.

In early interviews she was outspoken and unguarded, but learned not to be, which seemed a shame, because she was one of few MPs to have a common touch – a young woman with a good sense of humour, who could easily answer those what-was-the-last-album-you-bought? questions that make other politicians look like frauds. Even now, she gives the impression of being conspiratorial – she is likable and laughs a lot – but is mindful of what she says. Did politics change her? She nods. "Politics is too often about risk management, but if you ignore that you're dead, so I have become more risk-averse, which I hate, but it's my job. I have become more boring. Again, it's my job to be boring."

She describes losing her seat as "very bittersweet – at the time more bitter than sweet. But there were such huge upsides." Although she loved aspects of her job, the long hours, huge caseload and frustrating bureaucracy would also reduce her to tears. At the most stressful point, she was also undergoing IVF, which failed, and left her devastated. There were many times she wanted to resign but could never bring herself to do it. "I was single-minded about being a politician and I had some innate talent, but there are lots of people like that," she says. "You need more than that – you need luck. I had that luck, and to get there and be only the second ethnic-minority woman ever elected – at that point it becomes a responsibility. To walk away from it would have been heartbreaking." Still, at one stage her husband, miserable at never seeing her, wanted a divorce. "I got to the point where if I were to lose my career or my family, it would be my career that goes, and I will keep my husband and I will beg him and that's what I did. He still left." She laughs. "But he came back."

They have just celebrated 20 years together and adopted three children. She sits on the Lords select committee on adoption legislation, which has called on government to scrap a proposed change that would remove the importance of ethnicity when placing a child. "Saying a family is more important than race for a child in the care system is correct, but you don't want to go to the other extreme and say cultural identity is nothing," she says. "I was a mixed-race child brought up by a white mum – obviously it didn't impact very negatively on me, but it did bother me that people never thought she was my mum. What I now realise, with three adopted kids, is that they have issues of identity, as a result of adoption, that dwarf anything a non-adopted person has, so to add on top that you don't look like your family creates more complexity."

King also campaigned on the legal aid bill. "I've spent my whole life saying 'Don't vote Tory, you don't understand how bad it will be', and now I see the legislation that is coming through, I think I underplayed it. They're taking legal aid away from disabled children, women who are victims of domestic violence and workers who are ill and dying of, for example, asbestos-related disease. I feel very strongly about it. Access to justice is being eroded."

The Lords seems to suit her. Looking back at her career as an MP, she says, she was naive about how politics worked. She was often portrayed as a Blairite careerist; in reality, she says, "they thought – I mean Blair's inner circle – I wasn't reliable." She thinks it was one of the reasons she was never promoted; another was that "I didn't have a patron, and that's what you need. I just thought that if you worked hard and campaigned on important issues that was enough [but] you have to be connected, you have to have a senior cabinet minister banging on the table for you during a reshuffle and if you don't, you won't get anywhere. And I didn't."

Did she feel betrayed by Blair after she supported the war, a vote that ended her career as an MP? She thinks for a moment. "No, I don't think they owed me anything, I don't think I owed them anything. I don't have any hard feelings on a personal level. On a geopolitical level, I have very hard feelings." King has had to justify her decision so often that her reasoning sounds well practised – the intelligence failures and how they were presented were "unforgiveable"; she is "enraged" that the post-invasion planning was so bad, but she does not regret the removal of Saddam Hussein.

After the fight with Galloway, she would smile when people asked if she was scared of going up against Livingstone. She was realistic about her low chance of beating him, "but there's a place for democracy in Labour party politics and it's important to have a debate and selection, as opposed to an anointment". What she wasn't realistic about was how much it would cost: "I had to raise over £150,000 – if I had known, I wouldn't have done it; 75% of my time was taken up with begging people for money. It was humiliating."

In 2011 she held a fundraiser to pay off campaign debts, with an invitation that wryly claimed she was headed for bankruptcy. Really? "Well, I had no money. Where is anyone going to get £150,000 from? I did think I had made a terrible mistake [in standing] – I could deal with losing, but not with bankrupting my family." How close was she? Would she have lost her house? "I would have if certain people hadn't come out. I could have pulled out, but politically that's incredibly damaging, and I had so many people who had campaigned for me. How could I turn round and pull out?"

There was no crushing disappointment when she didn't win, she says. "I knew if I won I would have two years of campaigning – and I thought I had a chance of beating Boris Johnson – but if I lost I had a chance of my greatest dream of all, which was adopting a third child, and that's what I did. So if you ever see me holding my baby, you will know that I can have not one single regret."

Will she stand for mayor again? "If a week is a long time in politics, come on, 2016 is too far away, and the genuine thing is it depends on my kids. I still think the London mayor is the best job in the world, but that's a different question to whether I try to run for it again." It could be that she has her eye on a ministerial position should Labour win the next election, that Miliband could be the "patron" she lacked before – but she isn't ruling it out. Just like she never really ruled out appearing on a reality TV show.

[Written by Emine Saner and published in the Guardian Saturday 5 January 2013]