The British Museum is prevented by law from returning four Old Master drawings looted by the Nazis, even though it wants to hand them back to their Jewish owners' heirs, a judge has ruled.

Senior High Court judge Sir Andrew Morritt says that the 1963 British Museum Act, which protects the famous London-based institution's collections for posterity, could not be overridden.

Not even by a "moral obligation" to return works known to have been stolen.

The ruling was requested by Attorney-General Lord Peter Goldsmith, the Government's chief legal officer.

He had asked for clarification after warning that if there was a moral obligation to restore such objects it could give Greece a method by which to reclaim the Elgin Marbles.

The marbles are hundreds of marble sculptures taken from the Parthenon in Athens in 1801 and 1802 by British diplomat Lord Elgin, who later sold them to the British Museum.

Greece has long demanded the sculptures' return, something Britain is resisting.

Justice Morritt was asked to rule on the museum's obligation to return the four drawings by artists including Nicolo dell'Abbate and by Nicholas Blakey.

The paintings were stolen from the home of Dr Arthur Feldmann in 1939 when Germany invaded Czechoslovakia.

Dr Feldmann and his wife died at the hands of the Nazis, and the four drawings were acquired by the British Museum shortly after World War II.

A spokesman for the Commission for Looted Art in Europe, which is representing Dr Feldmann's heirs, says the judgement shows that Britain's Government should amend the law.

"The commission very much regrets that this avenue to achieve the return of the drawings is not now open to the museum," he said.

The museum agreed three years ago to return the artworks.