Bradley Manning, the intelligence analyst who is alleged to have leaked the thousands of state department cables, has often been compared to Daniel Ellsberg who leaked the Pentagon Papers in 1971.

But I have stumbled on a film in the archives that tells the story of another leaker in America who tried to do the same thing, but even earlier.

He was a young State Department diplomat who stole and copied thousands of Top Secret cables. Like Daniel Ellsberg, his aim was to release them to stop America’s involvement in what he believed was a disastrous foreign war.

He was called Tyler Kent. He was a diplomat at the US embassy in London in 1940 and he wanted to stop President Roosevelt bringing America into the war to help Britain.

It is a fascinating story, but it also brings an odd perspective to the contemporary Wikileaks story.

Tyler Kent was a horrible man. He was a rabid anti-communist who believed that the Jews had been behind the Russian Revolution.

He was convinced that Germany should be allowed to destroy both Communist Russia and the Jews. And America should not get in the way of that being allowed to happen.

Looking back, most people now feel that Daniel Ellsberg was right in 1971 because the Vietnam War had become a horrible disaster that needed exposing.

Today, we are not sure of Bradley Manning’s motives (and it hasn't been proven that he is the source of the leak), but again there is a general feeling that it was good thing because the cables have exposed an empty nihilism at the heart of America’s foreign policy.

But the perspective the Tyler Kent story brings is the realisation that diplomatic leaks are not automatically a good thing. It just depends on who is using them. And why.

Back in the past Tyler Kent wanted to use secret information to destroy the things that the overwhelming majority of the British people believed in and were prepared to fight for.

Back in 1982, Robert Harris tracked Tyler Kent down. He was living in a caravan in a trailer park on the US-Mexico border. Harris persuaded Kent to be interviewed and then made a film for Newsnight that told the story.

It is a great piece of historical journalism. Kent explains how his aim was to release the secret cables during the Presidential election campaign in 1940. Over 80% of the US population didn’t want to go into the war – and the cables showed President Roosevelt secretly promising Churchill help against Germany.

Harris makes a powerful case in the film that if Kent had succeeded America would not have entered the war. And history would have been completely different.

Tyler Kent himself is weird and mesmerising. But still unrepentently anti-semitic.

And the film also shows just how easily Tyler Kent found willing accomplices in the heart of the British Establishment. They wanted to get rid of the Jews and communists too, even at the expense of their own country.

The film begins on the morning of the 20th May 1940. Churchill had been sending secret cables to Roosevelt begging for American help.