British politicians today made their final pitch to a bitterly divided electorate on the eve a crucial referendum to persuade undecided voters of the merits of remaining in or leaving the 28-member EU with polls showing a razor-tight race whose outcome could shape Europe's future. In the biggest backing yet for the "Remain" camp, 1,280 business leaders, which included representatives of 51 FTSE 100 companies, signed a letter warning that Brexit - or Britain's exit from the EU - would mean "economic uncertainty and put jobs at risk". Also Read-\u00a0Brexit vote keeps investors on edge Their warning came on the last day of the four-month-long campaigning before polling booths open at 7 am local time tomorrow with the final result expected early on Friday. More than 46 million people are eligible to vote in the referendum in which people are being asked to choose whether the UK should stay in the European Union or leave in the first vote on the UK's links with Europe for more than 40 years. Opinion polls have suggested that while big business is broadly in favour of staying in the EU, small firms have been evenly split in what looks like a photo-finish with one poll showing "Remain" at 45 per cent and "Leave" 44 per cent, with 11 per cent undecided. Prime Minister David Cameron welcomed the support from top businesses as he kicked off the final hours of his campaigning, stressing that the UK enjoyed a "special status" within the EU and the "best of both worlds". Cameron, who has appeared alongside former Prime Minister John Major and former Labour leader Harriet Harman in Bristol, said that the decision will be irreversible and there will no coming back if the UK votes to leave. "You can't jump out the aeroplane and then clamber back through the cockpit hatch," he told BBC Radio 4's Today. Leaving the EU would be a "massive problem" for the UK, he said, doing "untold damage" to economic growth, jobs and family finances and hindering the opportunities and life chances of future generations. Speaking to the BBC, he said "We are not shackled to a corpse. You can see the European economy's recovery. It's the largest single market in the world. Making a personal plea to those who fear greater European control, he described himself as a "deeply patriotic person". "We have not been invaded for 1,000 years, we've got institutions that have served us well. I don't want to give that up to some sort of 'United Europe' and that's not what we're going to do. But Boris Johnson and other Leave campaigners said only a vote to leave the EU could give the UK the freedom it needs to set its own course, rejecting the economic forecasts suggesting the country would face a downturn following Brexit. The former mayor of London urged people to "believe in our country" and seize the moment.