LONDON — They are among the British moneyed elite: the head of the nation’s largest bank, a billionaire hedge fund manager and the owner of some of London’s most luxurious nightclubs.

Yet for tax purposes, they are not entirely British.

Thanks to a law from when Britain had an empire, a growing number of the rich and internationally mobile here do not have to pay tax on their foreign income or assets, only on the money they earn in Britain. They are the “non-domiciled,” or non-doms.

To qualify for that status, they simply need to show that their fathers were born outside Britain and that they intend to someday return to that place. Alternatively, they can choose a new permanent home — Hong Kong with its low tax rate is popular — return to Britain and demonstrate their intention to go back to their new permanent home by, for example, buying a grave plot there or drawing up a local will.

This Edwardian-era tax arrangement has returned to center stage. Questions are being raised as recent revelations that HSBC’s private bank in Switzerland helped clients stash money in offshore accounts reinforce a view that the wealthy play by a different set of rules when it comes to taxes.