UK business leaders, including Virgin Group founder Richard Branson and WPP chief executive Martin Sorrell, warned Prime Minister David Cameron in a letter to the Financial Times yesterday that he risks hurting Britain’s businesses if he proposes to exit the European Union.

In the letter, 10 signatories said more EU reform was urgently needed, but Britain had to be careful not to call for a wholesale renegotiation of its membership.

“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 said.

Other executives that signed the letter included Jan du Plessis, chairman of miner Rio Tinto, British Telecoms’s chairman Michael Rake and Chris Gibson-Smith, chairman of the London Stock Exchange.

Cameron has said that he wants to revamp Britain’s relationship with Brussels and is expected to set out his intentions in a speech later this month.

His increasingly vocal insistence on renegotiating terms with the EU has raised concerns that Britain may be heading for an exit. On Tuesday, Ireland, which holds the presidency of the EU , urged Britain not to be too adversarial in pushing for change in its relationship with the EU.