xii Introduction of a fruit machine spitting coins. In south-west London, I met Roland Riggs, who had served in Northern Ireland in 1971 and 1972. He cannot help glancing up as he walks down the high street, scanning for a slightly open sash window or missing roof tiles. He is on the lookout for snipers, more than forty years after leaving Belfast and Londonderry.

For many, the trigger is an anniversary – particularly of a comrade’s death.As the day approaches, a corrosive sense of guilt begins to creep in – the kind of guilt that can only be felt by those who have forged a bond under fire, then felt that bond break. Fireworks are a universal bane – the bangs and smoke reminiscent of gunfire and the smell of cordite. But for some the trigger can be as innocent as the twinkle of fairy lights on a Christmas tree – evoking the red or green diodes blinking on military equipment.

Sometimes the trigger is a word. For one soldier the mere mention of ‘Afghanistan’ sent him into a paroxysm of uncontrollable shakes.

On Remembrance Sunday, we drop a coin in a tin and pin a poppy on a lapel to honour the fallen. The ritual, begun by the Royal British Legion in 1921, ensures that the sacrifices made by generations of soldiers are not forgotten.Yet there are those among us for whom remembering is not a choice, for whom the boundaries between past and present blur, and for whom every day brings a fresh reminder. This book is about the British exservicemen and women still fighting wars in their minds.

The story is both very new and as old as war itself. From Homer’s Iliad and the plays of Shakespeare to Tim O’Brien’s stories of Vietnam in The Things They Carried, and The Yellow Birds, the novel by Iraq War veteran Kevin Powers, writers have explored the rage, alienation and melancholy that have followed soldiers home from battle.The centenary of the First World War has prompted a new wave of public fascination with the plight