"The Prime Minister said the UK greatly valued the investment of Japanese businesses into the UK, and we would do everything we could to promote and safeguard that investment in the wake of the referendum," a statement from Cameron's office said, following a telephone call between the two leaders.

"It would be important for Japanese companies to make their voices heard in the negotiations once they got under way," the statement added. Japan has major investments in Britain, notably by carmaker Nissan Motor Co Ltd in northeast England.

(Reporting by William James; Editing by Mark Trevelyan)