BRITONS vote today on whether to exit the 28-nation bloc which they joined in 1973, amid warnings from world leaders, investors and companies that a decision to leave would diminish the former imperial power's influence, unleash turmoil on markets and send shock waves through Europe and the wider Western world. In an address outside his Downing Street office, British Prime Minister David Cameron hammered home his message that leaving the EU would jeopardise Britain's economy and its national security, with fewer jobs, fewer allies and higher prices. As each side sought to play its last card, the pro-EU “Britain Stronger in Europe” campaign issued a final poster of a door leading into a dark void with the slogan: “Leave and there's no going back”. Opponents said the hastily arranged appearance suggested Cameron, who promised the referendum in 2013 under pressure from lawmakers in his party, was very worried about the outcome. Those arguing for Brexit have focused on what they say are pressures on public services and high immigration levels that cannot be reduced due to EU freedom of movement rules. In the same context, the Labour MP Jo Cox, a 41-year-old mother of two, was shot and stabbed to death while preparing for a constituency surgery in Bristall, West Yorkshire, this week. Her attacker, later identified as 52-year-old Thomas Mair, was said to shout “Britain first” while he attacked her. The killing led to a 48-hour suspension of campaigning for the referendum.