Its survey found that four out of 10 customers would happily sacrifice returns on current accounts if their bank operated in a more “green” or environmentally friendly manner.

The research also identified a gender divide — 47 per cent of women would accept a lower return if their bank invested ethically, compared to just 36 per cent of men.

Martyn Hocking, Edi­tor of Which? Money, said: “A significant number of people seem willing to accept lower returns on their money for banking ethically. But you don’t have to make a straight choice between ethics and value, as banks such as Smile offer the best of both worlds.”

Smile, the online arm of the Co-operative Bank, offers a current account that is a Which? Best Buy. Since 1992 the Co-op has said it will not lend to arms manufacturers or companies with bad environmental reputations.

Unfortunately, most high street banks do not have explicit ethical policies.

“If you want your bank to have an ethical lending policy, then write to them and say so, or switch to a
bank that does have one,” said Hocking.