With a Taliban fighter looming in his sights half a mile away, the British sniper knew a clean shot would take down his enemy. What he could not have known was that the single bullet he fired would account for five more insurgents. But, incredibly, his rifle round triggered the explosive vest worn by his target, killing all those around him. The record-breaking shot was fired by a Coldstream Guards marksman on one of the last missions to be carried out by British troops in Afghanistan. UK forces are preparing to leave their last frontline base in Helmand as part...