Anthony Eden, it was said, was thoroughly prepared for the job of prime minister. Unfortunately, he was prepared to do it in 1938 and didn't get it until 1955. Even Gordon Brown's worst enemies would not compare his premiership to the disastrous 19 months Eden spent in the job. (Actually, Brown's worst enemies, mostly former Labour ministers, probably would  they'd say anything about him.) But Eden and Brown both had a long, frustrating wait, and it damaged their premierships.

Brown watched Tony Blair use up the 10 good years, when, as Anthony Seldon and Guy Lodge point out in Brown at 10 (350pp, Biteback, £20), the economy was booming, Labour was riding high in the polls, and the Conservatives were fatally divided. Brown was left with the three harsh years. I am sure he knows that he did less with them than he and his supporters hoped. Now we have two accounts of how he handled his time to help us understand why.

Seldon and Lodge's book is big, thorough and painstaking. Few people will sit down and read it from cover to cover, but anyone seriously interested in modern British political history will want to have it around for reference. The authors have read everything and interviewed almost everyone, and tell the story in remorseless detail, week by week, sometimes hour by hour. Mostly they report, rather than tell the reader what to think, but that makes it treacherous when they let their prejudices loose.

One of these is that they evidently loathe Brown's ally and confidant Ed Balls. On their account, God and Satan seem in a state of permanent warfare for Brown's soul, and Balls is Satan's earthly representative. They can't mention him without a genteel shudder. Writing about emails from Brown's special adviser Damian McBride, calling for smears on opposition politicians, they call McBride a "wholly owned subsidiary" of Balls, which is a caricature of the truth. As they correctly point out, when Balls was education secretary he argued unsuccessfully with Brown for a break with Blair's education policy. If, like Seldon, your day job is running an expensive public school, that makes Balls an enemy.

As it happens, Balls gave the authors their best one-liner about Brown: "He is a complete confidence player. When his star shines, he thinks he can never fail, but when it does not, he thinks it will never light up again." That may be the key to the problems of his premiership. If you can damage his confidence, you can stop him from performing well, and political enemies sense that sort of weakness like blood.

Brown's confidence may have sustained a near-fatal assault in 1994, after John Smith's death. I am sure Brown must have kicked himself over and over again for not standing against Blair. He is a historian: he knows that there is almost no other instance of someone within touching distance of the top job in politics who decides not to run for it. He knows, too, that Nick Brown, who would have run his campaign, is sure he could have won it for him, if only he had given him the nod on the day Smith died.

When the crown finally came his way 13 years later, Brown spent far too much time and political capital trying to keep the diehard Blairites from attacking him  hence, for example, his doomed and ruinous attempt to win the EU presidency for Blair, recorded in compelling and grisly detail by Seldon and Lodge. He was never confident enough to tell the Blairites that their time had passed.

Keeping Brown's confidence up was part of what Sarah Brown tried to do in Downing Street. She is loyal, discreet and dignified, and she loves him. She has written a loyal, discreet, dignified, loving and, inevitably, somewhat boring book, culled from her diaries. There is no hint that she was ever consulted about important decisions, though according to Seldon and Lodge she was. The most frantic bits of Brown's government are dealt with in a laconic way oddly reminiscent of Mrs Dale's Diary. After reading Seldon and Lodge's densely written four-page account of the manoeuvrings that ended with Brown and his chancellor, Alistair Darling, nationalising Northern Rock, it felt odd to turn to Sarah Brown and read this: "It appears to be a busy day at both 10 and 11 Downing Street, and I keep a watchful eye on the news all day. At the culmination of many hours' work, the government has now taken over the running of Northern Rock as the only option left to keep it going. I have a cup of tea with Maggie [Darling] and we agree that both Gordon and Alistair are very calm and level-headed under the pressure."

Irritatingly, there's no index, which feels like the publisher's way of saying that this is a bit of ephemera, and no one's going to want to look anything up in it. Likeable though the book is, they're probably right.

Francis Beckett's Gordon Brown: Past, Present and Future is published by Haus.