In the dark days between the evacuation at Dunkirk and the impending battle of Britain the last thing the public needed, in Winston Churchill's opinion, was news of more catastrophes.

To maintain the momentum of the spin that the flight from French beaches had been a daring coup rather than a costly rout, the British media were banned from reporting that more than 100,000 British troops had been left behind and that efforts to rescue them had resulted in the greatest maritime disaster in British history.

The story has remained buried, in effect, to this day. In this his fourth book, former South China Morning Post editor Jonathan Fenby draws on interviews with veterans and a wide range of historical records such as the oral history tapes of the Imperial War Museum to set the record straight.

Fenby presents his material as a vivid patchwork of recollections, which he drapes across a skeletal historical frame at once substantial enough to give perspective yet too light to impose textbook gravitas. Each vignette is concise, replaying brief seconds of history. Hung so dispassionately and so dissociated, their poignancy is captivating.

In the first part of the book we meet some of the abandoned soldiers destined to become passengers on the doomed ocean liner Lancastria. The German blitzkrieg rolls across Europe, pushing a wave of refugees and fleeing troops before it. We blunder aimlessly with them as they cross the unoccupied western regions of France, drinking wine, flirting with farm girls, despatching a wounded child with a service revolver rather than watch him die in agony, stumbling into German patrols, sometimes killing, sometimes losing comrades, never knowing what's around the next corner.

In the second part of the narrative we join them as they board the converted Cunard liner. It's stuffed beyond capacity with 6,000 troops, more than half of whom are to die when the ship is sunk en route to England, too many in the most gruesome and tragic ways.

We dive with a German bomber pilot at the 'fat freighter' he recalls lining up in his sights. Four bombs score, and the ship bursts 'like a child's tin drum struck with a hammer'.

Fighter planes roar overhead, machine-gunning survivors as they float in a flotsam stew of oil, debris and body parts. A dog swims past. An officer shoots a man whose panic threatens to topple a lifeboat. A stairway collapses under the weight of stampeding troops, condemning all those inside. Six months later, bodies still appear in the nets of local fishermen.

For most of us, the second world war is just a faded collective memory. But for the last survivors of the Lancastria, who still meet once a year, it remains a searing horror. Their memories are a sobering reminder of just how much misery my generation escaped by being born a few decades later than theirs.