JP Morgan, the biggest bank in the US, has hinted it could quit the UK if Britain votes to leave the EU.

The warning came as a number of US investment banks lined up to offer financial support to the In campaign. The bank’s chief executive, Jamie Dimon, said: “Britain’s been a great home for financial companies and [EU membership] has benefited London quite a bit. We’d like to stay there, but if we can’t, we can’t.”

JP Morgan employs about 19,000 people in the UK, with its main offices in Canary Wharf, Bournemouth and Glasgow. The bank employs Tony Blair as an adviser.

Dimon was speaking on the sidelines of the annual World Economic Forum in Davos as it emerged that the bank is offering cash support to the Britain Stronger in Europe campaign.

On Wednesday, it was revealed that Goldman Sachs has also pledged several hundred thousand pounds to the campaign. Morgan Stanley, which employs about 5,000 people in Britain, is understood to be planning a donation and Bank of America is reported to be considering doing so too. Dimon’s suggestion that JP Morgan might quit the UK came as David Cameron called on business chiefs attending the Davos meeting to support him in keeping Britain in the 28-member union.

“I hope that businesses and NGOs and other organisations don’t hold back,” he said, urging them to make their views known before official campaign period gets underway. This is a once-in-a-generation moment and the stakes are high,” he said.

“If you want a more competitive Europe, where the single market is completed, where there are more trade deals and fewer regulations: join me in making that case. If you believe, like I do, that Britain is better off in a reformed European Union, then, when the time comes, help me make that case for Britain to stay.”

Cameron has promised an in/out referendum by the end of next year, when he has completed renegotiations with Brussels. He aims to secure a reform deal next month but said he was in “no hurry” and would wait until the end of next year to hold the vote if necessary.

Dimon refused to detail the exact scale of JP Morgan’s donation to the in campaign but it is likely to be a significant sum of money. He said: “We’ve just starting. [I] wish we didn’t have to do it at all.” He added: “I can’t tell the British people what to do, it’s up to them.”

The bank’s plans to donate to the in campaign mean Wall Street could contribute millions of dollars to influence the vote while Britain’s banks do not. Barclays’ chairman, John McFarlane, has spoken in favour of Britain staying in the EU but Barclays’ policy is not to make political donations.

Allie Renison, head of Europe and trade policy at the Institute of Directors, said it was not clear whether the US banks’ intervention would benefit or harm the In campaign. “These businesses employ thousands of people in the UK and businesses from outside the UK may be seen as having more credibility because they take an independent view. But I think it will be something the Out campaign is able to use to argue that staying in the EU is in the interests of big corporates, not all companies.”

Nigel Farage, the Ukip leader, described the donations as “the unholy alliance of big banks and big politics”.

However, not all business leaders at Davos agree that a Brexit would be problematic. Carlos Ghosn, the chief executive of Renault-Nissan, told the Guardian he was unworried about the prospect of an out vote. Ghosn said: “ Whatever is the decision of the UK we will adapt to it. I don’t think there is a reason to worry. We knew for many years that [an exit] was possible. So we’ll deal with it”.

The US banks are free to make donations now because the rules of the referendum have not been set and the campaigns are not officially registered. Once the rules are established, businesses’ ability to contribute may be restricted. US investment banks have based their European operations in London since the 1970s. They then made the City the centre of their international operations partly because of the UK’s position between the time zones of Asia and the US.



Moving operations to countries such as Ireland, France or Germany would be disruptive but the banks say they may have to do so if Britain no longer has the necessary trade agreements with the EU.

The future of Europe has been debated among the 2,000 delegates to the annual gathering in the Swiss Alpine ski resort. The French prime minister, Manual Valls said it would be a “tragedy for Europe” if the UK electorate voted to leave. He added: “We must find a compromise, and everyone must contribute to it.”