Perhaps Powell couldn’t resist the opportunity to compare Gordon Brown to the great classical villains cited by Machiavelli, but the frame sometimes feels laboured. One moment you are engrossed in an account of how the Sun turned on Gordon only to turn the page into a siege in Renaissance Italy.

Machiavelli is here to provide a historical authority and a narrative framework for Powell’s own valuable lessons. He really wants to set key New Labour controversies – spin, the TeeBee-GeeBees, party funding, sofa government – in a more sober setting. The result is fascinating. For students of government, Powell considers issues like the limited value of inquiries in either satisfying the mob or getting to the truth. For the political obsessive, there are great anecdotes, such as Blair accidentally offering to perform the karma sutra on French prime minister Lionel Jospin.

However, as a former special adviser, it is Powell’s lessons for servants, not princes, which stand out from this book. His descriptions of the battles against the ‘passive resistance’ of the civil service feel familiar, but what sets Powell’s book aside from other recent New Labour memoirs is the description of the relationship between adviser and principal.

Powell is strikingly honest about the price you pay to be an effective adviser. This is not just a matter of interrupted weekends or lost evenings as you toil to deliver your leader’s wishes. He describes a professional existence where you must simultaneously project total confidence while living with the vulnerability of being contradicted in any judgement you make. Your job, Powell writes, is ‘to absorb pain’ and to act as a ‘barrier between his anger and fear and the rest of the world’.

The lessons here should be read by any would-be consigliere. If Gerald Kaufman wrote the book on How to be a minister, this is a contender for How to be an adviser.