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Prince Philip privately supported nuclear disarmament during the Cold War despite his key role in the military.

Newly declassified documents have revealed the Duke of Edinburgh, who retired from public life earlier this year, believed the Cold War arms race was "ridiculous".

Like other members of the royal family Prince Philip is expected to stay out of politics.

Letters between Prince Phillip and Lord Brockway an outspoken Labour MP and an anti-nuclear activist revealed by the Times, show that the Queen's consort backed multilateral disarmament.

The revelations may come as a surpise to many because of Prince Philip's ardent support for the armed forces.

He saw active service in the Second World War and served as the ceremonial head of the Royal Marines for more than 60 years.

On February 12, 1981, Lord Brockway wrote to Prince Philip enclosing a copy of a speech by Earl Mountbatten, the duke's uncle, which he had given to the Stockholm International Peace Research Institute in May 1979.

(Image: AFP)

The Earl's speech concluded: "As a military man who has given half a century of active service, I say in all sincerity that the nuclear arms race has no military purpose. Wars cannot be fought with nuclear weapons. Their existence only adds to our perils."

The duke replied, five days later, writing: "Dear Lord Brockway. Thank you for the copy of Lord Mountbatten's Stockholm speech. I agree with everything he said. I agree that the arms race is ridiculous."

The duke also claimed newspaper reports had misrepresented comments he made when delivering the inaugural Earl Mountbatten lecture at the Cambridge Union on February 9, 1981.

Lord Brockway wrote to the duke after hearing suggestions that he believed that a "successful defensive nuclear war" was feasible.

(Image: Hulton Royals Collection)

In his response, the duke wrote: "I said I was in favour of multilateral disarmament and the SALT (Strategic Arms Limitation Talks) Treaties.

"I added that it was possible that there had not been another major war in the last 30 years because world leaders realised what a horror they would unleash on the world."

(Image: AFP) (Image: Daily Mirror)

Lord Brockway's private correspondence with the duke was donated to the nation.

It was due to remain closed until 2022, but has now been opened to the public and placed in the National Archives at Kew after a routine review.

Prince Philip ended his active naval service in July 1951. He remains Lord High Admiral of the Royal Navy but stepped down as Captain General of the Royal Marines this year.