A group of business leaders have warned the prime minister against his expected call for a renegotiation with the European Union.
Senior figures including Virgin's Richard Branson, BT's Michael Rake and Clifford Chance's Malcolm Sweeting used a jointly penned letter to appeal to David Cameron ahead of the PM's much-anticipated speech on Europe.
Writing in the Financial Times, they warned of the dangers of destabilising Britain's relationship with the EU. The UK's involvement in the single market directly affects the status of one in ten jobs in Britain.
"To call for such a move in these circumstances would be to put our membership of the EU at risk and create damaging uncertainty for British business, which are the last things the prime minister would want to do," the letter's signatories wrote.
"The EU remains home to half our exports and is the most powerful trading bloc in the world.
"Other EU member states are the main source and destination of foreign direct investment into and from the UK, accounting for about half of our investment."
Cameron has so far resisted pressure to guarantee an in-or-out referendum under a Conservative government after the next general election.
But intense pressure from eurosceptic Tory backbenchers and the growing threat from Ukip have forced the Conservative leader to prepare for a major shift in his traditionally balanced approach to the issue.
Cameron is expected to use his Europe speech to call for a comprehensive reassessment of Britain's relationship with the EU. The results of the process would then be put to the British public in a referendum at some stage in the next parliament.
Speaking at the weekend, the prime minister said: "People should be in no doubt the Conservatives will be offering a real choice and a real way of giving consent to that choice."