So, did Oona King have an affair with Jack Straw? From the evidence on display here, probably not, but the notion of the former MP blushingly discussing the rumours of their affair with the then home secretary behind the dispatch box is one of the more startling in this candid memoir.

Oona King was elected MP for Bethnal Green and Bow in the Labour landslide of 1997. Just 29, she was one of “Blair’s Babes”; naturally, perhaps. She was only the second black female MP, and people expected great things of her. Her diaries are an account of how it all went wrong. Although the book is full of hilarious set pieces – meeting Blair moments after covering her hands with hair ointment, being tongue-tied seconds after standing up to speak in the House – what reverberates is not the comedy of a series of scrapes but her sense of aching disappointment for a career manqué.

The book takes 50 pages to kick in, after King has given us her life and times at York University, her love of raving and a description of her wedding dress: “a silver baby doll with matching silver platforms and an eight-foot veil”. When the diary finally starts, there are so many lacunae it is impossible to read it as a daily journal. It is more a staggered sequence of episodes of high drama: we follow King’s travails as earnest back-bencher and, at one juncture, as environmental saviour, journeying up the Congo on a canoe to spend 15 minutes with a bunch of disaffected pygmies.

The trouble is that King, who has wanted to be an MP since the age of five, is just too worthy about the whole business of democracy. Rashly, she thwarts the prime minister and defends Ken Livingstone’s right to stand for mayor of London, thus casting herself into permanent Blair purdah. (Naturally, Ken manages to stitch her up several years later.) She refuses to do various career-enhancing jobs around the House because she will commit only to causes she believes in. She will not do television unless she can talk about housing or genocide. She jeopardises her marriage by insisting on working through the night, composing personal letters to every constituent who writes to her. She votes against the government more times than is wise. And then she has the naivety to complain when she sees others in her “year”, clearly far more pragmatic than she is, winning positions of power. While her friend David Lammy is having his engagement party hosted by Charlie Falconer in the lord chancellor’s private residence, and her peer Ruth Kelly is promoted to the cabinet, King is left handing out parliamentary questions in the tea bar. “My job, from a parliamentary perspective, could not be more dull, repetitive or low-skilled. In fact, the more correct term is unskilled,” she writes sadly. She is so out that one wonders how she manages to hold her head up at all in the House. No wonder that when George Galloway comes after her parliamentary seat – pointing out to her Muslim constituents just how Jewish she is, among other things – she is abandoned to her fate.

In spite of the worthiness, one can’t help liking King. She is married to a total toerag, the Italian demigod Tiberio, whom she describes as a walking sex symbol, but who is low enough to do things like ring her up at work and toy with dumping her when John Prescott is walking past. She has to open a centre for birth control while experiencing a miscarriage (after her fifth failed IVF cycle). She is no stranger to human error, turning up at the wrong venue to give a speech and leaving her pager behind at a petrol station when No 10 is about to call. (No 10 did call, and the petrol-pump assistant called No 10 back, to her horror.) Her diary reads like a string of escalating disasters, culminating in humiliation by the merciless jaws of Galloway at the general election in 2005.

Yes, it’s a trifle smug, and I could have done without the “I am a committed constituency MP, knocking on doors in Tower Hamlets” stuff, not to mention the “all journalists are scum” riff that runs through it. But King is nothing if not spirited. The book has eyewatering details about working in the House (90hour weeks, bullying, bitching) and will be enjoyed by anyone who has ever tried to operate in the British capital when every parking spot seems to have conspired against you, and life throws up seemingly impossible challenges (in King’s case, Tracey Emin shouting at her in an open meeting, while waving a brick). By the end, I’d come to admire King, a woman with considerable public profile who grabs antidepressants from her aunt to stop herself bawling in the corridors of the House of Commons, who is able to admit failure and who – now that her life’s ambition is in tatters – is seriously considering teaching aerobics to pensioners.

Buy HOUSE MUSIC: The Oona King Diaries by Oona King
Bloomsbury £12.99 pp373

Times Recommends

• Superfreakonomics by Steven D Levitt and Stephen J Dubner
• The Times picks the 50 best paperbacks of 2009
• Vincent van Gogh’s letters show the soul of the artist