Keir Starmer stands on the cusp of becoming prime minister despite being a puzzle to many in Westminster and beyond who really don’t understand how he has got there, let alone who he is or what he wants to do if he makes it through the front door of 10 Downing Street.

This authoritative – but not authorised – biography by Tom Baldwin provides answers by drawing deeply on many hours of interviews with the Labour leader himself, as well as unprecedented access to members of his family, his oldest friends and closest colleagues.

Together, they tell an unexpectedly intimate story filled with feelings of grief and love that has driven him on more than any rigid ideology or loyalty to a particular faction.

The book tracks Starmer’s emergence from a troubled small town background and rebellious youth, through a storied legal career as a human rights barrister and the country’s chief prosecutor, to becoming an MP relatively late in life.

Baldwin provides a vivid and compelling account of how this untypical politician then rose to be leader of his party in succession to Jeremy Corbyn, then transformed it with a ruthless rapidity that has enraged opponents from the left just as much as it has bewildered those on the right.

Above all, this is a book that should be read by anyone who wants to understand how someone who has too often been underestimated or dismissed as dull, now intends to change Britain.