David Cameron urged Angela Merkel on Friday to help keep Britain in the EU, amid concerns in senior Tory circles that many hedge fund chiefs will throw their financial muscle behind the "Brexit" campaign.
The UK prime minister entertained the German chancellor at Chequers with a dinner intended to accelerate his EU renegotiation, which is making slow progress in Brussels.
Mr Cameron's allies fear that the longer the talks drag on, the easier it will be for Brexit campaigners to make the political running, partly funded by eurosceptic hedge fund executives.
While several hedge fund managers have been big donors to the Tories, Crispin Odey, a leading hedge fund manager, supports the "Vote Leave" Brexit campaign, launched on Thursday night. "The hedge funds are resolutely anti-EU," said one leader of the pro-EU campaign.
Mr Cameron expects much of corporate Britain to support Britain's continued membership of the EU.