text: Tesco chairman John Allan claimed David Cameron's decision to promise an in-out referendum before knowing what powers can be clawed back from Brussels means the cart is very firmly before the horse' Tesco could quit London if Britain leaves the European Union, its chairman has warned in a swipe at David Cameron. John Allan claimed the Tory leader's decision to promise an in-out referendum before knowing what powers can be clawed back from Brussels means the cart is very firmly before the horse'. He suggested large firms like the supermarket giant could move their head offices from London to other sites in Europe 'relatively painlessly', should Britain exit the EU. The Tory election manifesto includes the promise of an in-out referendum by 2017, but only after reform of Britain's membership. It states: 'It will be a fundamental principle of a future Conservative Government that membership of the European Union depends on the consent of the British people – and in recent years that consent has worn wafer-thin. 'That’s why, after the election, we will negotiate a new settlement for Britain in Europe, and then ask the British people whether they want to stay in the EU on this reformed basis or leave. 'David Cameron has committed that he will only lead a government that offers an in-out referendum. We will hold that in-out referendum before the end of 2017 and respect the outcome.' But in an interview with the Independent on Sunday, Mr Allan warns this approach risks backfiring, because it commits to a referendum regardless of whether a better deal has been struck with Brussels. He suggested that a better approach would have been to lobby for reforms first, and then set a date for a referendum. He said: 'Logically, you would have started with 'these are the reforms we would like to see enacted within the EU' and then, at the end of the process, determine whether or not you've made enough progress and then decide if a referendum is necessary.' He said the idea that a referendum will be held in 2017 if a Conservative government comes to power next month could have a real impact on people's investment decisions. 'It's a question of weighing up the pluses and minuses. This issue of the EU referendum and the uncertainty that it creates and the possibility that it could lead to Britain leaving the EU is a particularly heavy kind of pebble to put in the scales,' he told the paper. David Cameron, pictured today, has promised to renegotiate Britain's membership of the EU before holding an in-out referendum by 2017 . Mr Allan, who described his political leaning as being 'pretty close to the centre', was not among the more than 100 senior business leaders who signed an open letter last month praising the Tory Government and warning that Labour could 'put the recovery at risk'. He said he did not think it was advisable to 'choose sides' as firms will have to work with whichever party or parties form the next Government. Mr Allan also warned the political parties to be careful in their approach in dealing with the issue of immigration, saying they had been 'spooked' by Ukip into making declarations on the issue. 'There are problems ... that need to be sorted out, but I think the answer is not to lock the door and throw the key away,' he said. Labour leader Ed Miliband issued a plea to Tory voters worried about leaving the EU to back him instead. In an interview with The Observer he said: 'I am a politician of the left, but I am positioned where the mainstream of politics is positioned. I am on the centre ground of politics,' 'I want to reach out to Tory voters, to Liberal Democrat voters, to Ukip voters, to non-voters ... to people who feel that David Cameron can't answer the challenge of our time, who worry about our place in the European Union, who really think to themselves, 'we can do a lot better as a country'.'
target: John Allan suggested Tesco could easily move its HQ out of London .
  Cameron has promised to renegotiate Britain's membership of the EU .
  An in-out referendum on the outcome of the talks would be held by 2017 .