The Queen and the Duke of Edinburgh attended a moving service at Westminster Abbey, one of many events being held in memory of the fallen soldiers.
In France, the Duke and Duchess of Cambridge were joined by Prince Harry for a vigil at the Thiepval Memorial, where the 70,000 British and Commonwealth soldiers with no known grave are commemorated.
The moving services come on the eve of the centenary of the start of the Somme offensive. On July 1, 1916, following a seven-day British bombardment, some 120,000 men clambered from their trenches and went 'over the top' — to be met by a hail of German machine-gun fire that mowed down half of them. With 20,000 dead and 40,000 wounded, it was the bloodiest single day in British military history.
By the end of the four-month battle in northern France, more than a million soldiers had been killed and wounded on both sides. The First World War would drag on for another two years.