Andrew Mitchell, as he readily admits, was born into the British Establishment. Almost from birth, his path was marked out: prep school, public school, Cambridge, the City, parliament, the Cabinet. At every step along the way he acquired the connections that would propel him to the stratosphere. But for one extraordinary event, who knows where he might have ended up? Certainly in one of the top jobs.

In other circumstances this might have been a conventional story. Posh boy goes into the City, makes loads of money and then takes time out to come and govern us. In fact this is an unusual memoir — honest, self-deprecating and rich in anecdote. A fundamental streak of decency runs throughout.

Mitchell’s family made their money in the wine trade — they owned El Vinos. After a year as a junior army officer and several years in banking with Lazards, he was elected to parliament, aged 31. His father, a minister in the Thatcher government, was already there. The early years were conventional: a spell in the whips’ office, followed by a couple of years as a junior minister. He lost his seat in the Labour landslide of 1997 but soon returned, this time for ultra-safe Sutton Coldfield. Although initially not in the Cameron camp, he found himself on the Tory front bench as international development spokesman.

Ordinarily this would not be seen as a particularly good career move for an up-and-coming Tory, but having lost three successive elections, the Conservatives were in the doldrums and Cameron was determined to shake off their reputation as ‘the nasty party’. By contrast, international development was a Labour success story. Moreover, this was one of the few areas where, to use a phrase beloved of jingoists, Britain really did punch above its weight.

Mitchell, with Cameron’s backing, went about the task with enthusiasm. They endorsed Labour’s commitment to meeting the UN target for development aid — 0.7 per cent of GDP — and undertook to preserve international development as a separate government department. As evidence of sincerity, they set up a series of specifically Tory aid projects in Rwanda. The aim was not only to demonstrate commitment but to build a cadre of younger, more idealistic Tories who cared about the wretched of the Earth.

In government Mitchell duly became secretary of state for international development, even turning down promotion in favour of staying where he was. After two and a half years he was reluctantly persuaded to become government chief whip. At this point catastrophe struck. Emerging from Downing Street on his bicycle, he became involved in a heated altercation with police officers who declined to open the main gates and instead suggested he exit via the pedestrian entrance.

Within days all hell had broken loose. The police note of the incident had somehow found its way into the media. Most damaging of all was the allegation — hotly denied by Mitchell — that he had described the police officers concerned as ‘plebs’. Thus was born Plebgate. The story would not die, despite repeated apologies.

Mitchell and his family were under siege. For more than 30 days reporters camped outside their home. Others harassed his aged parents. He was spat at in the street. So intense was the heat that he was eventually forced out of office. Later, one of the key witnesses, an off-duty police officer, was found to have been lying and subsequently jailed; four police officers were dismissed for their part in the affair and several others disciplined. At which point Mitchell made the fatal error of suing his tormentors at the Sun, and he in turn was sued by the one police officer against whom no misconduct was proven.

He thus found himself up against two of the country’s mightiest vested interests — the Murdoch press and the Police Federation — and lost ‘on the balance of probabilities’. Damages and costs came to around £2 million. A minor incident that lasted no more than 45 seconds brought him to the edge of ruin. He describes the impact on himself and his family: ‘By Day 4, driven out of our home, I couldn’t sleep. I stopped eating and started smoking again… I lost about a stone in three weeks. On several days I couldn’t get out of bed.’

All was not quite lost, however. Friends rallied round. His constituency party stuck with him, and he has since carved out a useful role on the backbenches as one of the few genuine internationalists in the upper reaches of the modern Conservative party. Once again (for the third time in the past 50 years) the Tories have wound up the international development department and its budget has been slashed. Assurances from Boris Johnson on the subject proved worthless. Mitchell, a sadder and a wiser man, says: ‘I have resigned from the British Establishment.’