Thiepval - Britain and France recalled the horrors of the Battle of the Somme on Friday, 100 years after their troops fought and died together in one of the defining offensives of WWI.Britain's royal family, Prime Minister David Cameron and French President Francois Hollande took part in a commemoration at the Thiepval Memorial in northern France to remember the one million who were left dead, injured or missing in the 141-day battle.Guards of honour, bagpipes and military bands accompanied the moving ceremony in the shadow of the imposing memorial inscribed with the names of 72 000 servicemen who went missing in the surrounding fields.However, modern political battles could not be ignored, and Hollande had a brief exchange with Cameron after the ceremony, a week after Britain voted to leave the European Union."The decision has been taken, it cannot be delayed or cancelled," said Hollande, who made a last-minute change to his schedule to attend the ceremony. Hollande said a speedy Brexit "would avert all the uncertainties and instability, especially in the economic and financial domains. The faster it goes, the better it will be for them"."I want to recall that it is the European idea which allowed us to overcome divisions and rivalries between states, and which has brought us peace for the past 70 years," he said in an earlier statement.During the ceremony narrators, using old letters, poems and songs, took about 10 000 guests – who scrambled to pull on plastic ponchos as the clouds burst – through one of the deadliest battles of all time."There [were] high explosives, shrapnel, everything you can imagine. Terrific, hurtling death," read a letter from Private Sean Fendley of the British Army of the first time soldiers went "over the top" to face their German enemy.The offensive was launched to ease pressure on French forces taking a hammering at Verdun, and was preceded by the largest artillery bombardment in history, with about 1.5 million shells lobbed at the Germans.However, this was not enough to break German defences, and of about 55 000 soldiers who scrambled out of their trenches, 20 000 would be dead by the end of the first day of fighting – the bloodiest in British military history.Failures of European governmentsThe Battle of the Somme was a tragedy not only for British, French and German troops, but also Commonwealth nations whose soldiers fought for Britain.Guests from South Africa, New Zealand, Australia, India, Pakistan, Canada and Ireland also attended the event. Germany was represented by former president Horst Köhler.The commemorations began with the blast of whistles on a former battlefield and in Parliament Square in London at 07:30 sharp to mark the start of the offensive.The previous night, Queen Elizabeth attended a night-long vigil in Westminster Abbey while her grandson Prince William was in France along with his wife Kate and brother Harry for a vigil at Thiepval."We lost the flower of a generation, and in the years to come it sometimes seemed that with them a sense of vital optimism had disappeared forever from British life," said William."We acknowledge the failures of European governments, including our own, to prevent the catastrophe of world war."By the time the battle ended on 18 November, the frontlines had only moved a few kilometres, and the attritional battle became a defining event in the war, symbolising the horrors of trench warfare and the futility of the conflict.It was also the first battle in which tanks were used.A place of ruin and deathPrince Charles narrated an account of the devastated battlefield from the writer John Masefield."There is nothing white, nor alive, nor clean, in all its extent; it is a place of ruin and death, blown and blasted out of any likeness to any work of man, and so smashed that there is no shelter on it," he said."All wars end; even this war will someday end, and the ruins will be rebuilt and the field full of death will grow food, and all this frontier of trouble will be forgotten."A century on, the eerily calm, bucolic Somme farmlands belie the slaughter wrought there, and are now the haunt of tourists who come to visit about 400 war cemeteries across the region, and the overgrown warrens of trenches.