The year is 1992. John Major has just won an election and will become, in due course, the most unpopular prime minister since polling began. Edwina Currie's second volume of diaries opens with her being offered a job in the new government. The level of detail is unwarranted: anecdotes that were not of much consequence to begin with (she didn't want the job, asked if there was anything else, and they said no) are rendered perverse with intricacy ("I was phoned at Findern at 12.50pm; I'd been in the office at Swad since 11am, and the kids were at home …"). The inner workings of her mind are depressingly mercenary – she wants to be an MEP because the "weather is better, the money is interesting and the food both". She wants to write a "serious novel based in Westminster" (it turns out she means A Parliamentary Affair), because it would be "a challenge, could be fun, and might just sell a bit".

She will tell you the price of absolutely everything. Sometimes it's high spirits, such as the meandering paragraphs in which publishers bid for her "serious book". Other times I suppose there's a point to it – she explains her desire to leave parliament partly by the fact that she can't afford school fees on her salary, and so bestows the dignity of motive on an otherwise unreflective stream of huffing and moaning. But often it is just straight itemisation, every in and every out, from 50p per book in royalties to £150,000 earnt in the year 1995-96, to £2.50 "(outrageous!)" spent on a pint of Becks. This has a kind of Brechtian alienation effect, a constant reminder not to become emotionally involved with the narrator because she has monetised her interior life. All that's going through her head is: "I look nice, I'm sure that Königswinter industrialist fancies me, I bet he'd be head over heels if I bought this bra in peach cashmere … TWO HUNDRED AND HOW MANY DEUTSCHMARKS?" Never is a belief in the supremacy of the market less helpful than when you're trying to tell a story.

This isn't to say that the book is totally unengaging: Currie's style is arch and straight-talking, full of sideswipes ("it's such a pity that I can't stand her", of Virginia Bottomley), open attacks (on everyone whose success she ever felt displaced by – which is pretty much everyone in her party), derision (for everyone in any other party) and, when all else fails, a snide remark about someone looking fat or dowdy. It's so downright unpleasant at times that you peer in for the seam of a joke, but you'd look long and hard (she berates Shelagh Roberts for fighting and losing a European seat while she was ill: "What a remarkably brave woman – but it would have been better for the party … if she had allowed someone else to fight it"). Other times, it's so sentimental that, again, it's hard to take it at face value. Sitting down to begin writing her parliamentary bonkbuster (which, with hindsight, was most probably intended as a warning to John Major), she writes: "I've ordered a new computer, faster and quieter and lighter than the old one … Please God, support me and help me find a voice." Why would God, of all people, support such an endeavour?

That is all quite diverting, though you'd have to be interested in early 90s politics to a pathological degree to plough through 300 pages of it. It's not the length that makes it deadly, so much as the pointless detail combined with a lack of self-awareness, the first doubtless a consequence of the second, since nobody who'd ever given one minute's thought to whether they were adding to or depleting the sum of human happiness would ever write: "The chimney breast in the study is also wet and a bit smelly. So we haven't finished here yet." She makes this telling remark after a shopping trip: "I look stunning in Balenciaga and Ungaro and Karl Lagerfeld, but … the Chanels and Yves St Laurent looked ordinary."

Throughout, when things go well, it's because she's stunning; when they go badly, it's because someone else is ordinary. After all that fussing about school fees, her older daughter does poorly in her A levels. "This against a background of a record national entry and a record 80% getting A, B or C [Debs got a C and two Ds]. So Denstone [the school] has a lot to answer for." It never occurs to her to look for fault in her own daughter, and neither does it give her a second's pause about private schools being, just possibly, a giant waste of money.

There are ideas that I can't help thinking were added after the fact – it's true that she is on record as wanting to bring down the age of consent for homosexuals but it seems improbable that many of her close friends died of Aids, as she claims. I also doubt that anybody who had thought deeply about sexual politics in this era would use the phrase "HIV positive" as a noun (yes, really: "On Tuesday Margaret [Thatcher] herself had derided the whole business by saying she had had scrambled egg for breakfast that morning. She might just as well have said she slept with an HIV positive at the height of our Aids campaign").

Oh yes, the politics – various paragraphs overflow with names, all footnoted so that we learn what constituency they held but nothing else. Dramas are called "exciting": no evidence appears. Indignation burns from the prose, but there's no insight or reflection, which makes it sour and underpowered, like bitching about people who are dead.

But John Major – he's still alive, if anything more convincingly so now than he was then. Currie's feelings for him are contradictory; she is bitterly resentful of almost everything, from being offered the wrong job to being served some unsatisfactory lamb. And yet, catch her late-night reveries and she could well be thinking "Funny how I used to wait at this hour for a visitor! He might be performing better elsewhere if he still came to see me", as though she were some sort of fluffer for conservatism. As much as this is a book about all the brilliant things she's done, it's a book about all the things that would have been better if she'd done them. Remembering the Major government, it's hard to conceive of its having been worse; but that's about as far as I can travel with this analysis.