Scotland Yard said it had been advised by the Crown Prosecution Service that there was insufficient evidence to prosecute the man under the War Crimes Act 1991.

Although they did not name the man, it is known that the investigation concerned Anton Husak, who now lives near Cardigan, west Wales.

Death squad claims

Detectives had been investigating what part Mr Husak may have played in a Nazi death squad that murdered Jews in Eastern Europe.

Mr Husak was on a list of suspected war criminals supplied to the UK Government by the USSR in 1988.

He was specifically alleged to have taken part in three massacres killing thousands of Jews.

However, a Metropolitan Police spokeswoman said: "We have been advised by the CPS that there is insufficient evidence to provide a realistic prospect of conviction in this case under the War Crimes Act 1991.