A British general kept Winston Churchill and Free French leader Charles De Gaulle in the dark about a top secret 1942 plan to arm Vichy France, recently discovered documents reveal.

Both Churchill and De Gaulle had made clear their contempt for Marshall Petain's regime, which controlled a large part of France thanks to a deal struck with Hitler.

Relations between Britain and France had been strained since July 1940, when Churchill, who was determined to stop French ships falling into German hands, ordered the Royal Navy to sink several French war ships off the coast of Algeria - 1,300 French sailors lost their lives in the action.

In retaliation, a furious Vichy not only broke off diplomatic relations with London but also bombed Gibraltar.

In December 1941, Winston Churchill made clear his distaste for the supposedly neutral Vichy regime and its often enthusiastic collaboration with Hitler.

Here we were having been fighting the Vichy French... and here we are talking about arming their colleagues Professor Eric Grove, University of Salford

"The men of Vichy, they lay prostrate at the foot of the conqueror, they fawned upon him," he said, in a speech to the Canadian Parliament in Ottawa.

Later, Vichy voluntarily deported Jews to Germany.

Charles De Gaulle was equally contemptuous. Vichy's leaders had accused him of being a traitor when he fled to London after the fall of France. At the time, Marshal Petain, a hero of World War I, was a more popular figure in France - many saw him as having shielded Vichy from the worst excesses of Hitler's forces and saved the region from German occupation.

But neither man had anything to say about a secret meeting in London in December 1941 between a senior Vichy military officer and a member of the British General Staff. That, it seems, is because nobody told them.

But documents dated six months later show that the meeting resulted in a decision that was both extremely significant and highly controversial.

Image caption General Alan Brooke's Most Secret memo of May 1942: "Plan to give support to the French Army in occupied territory"

A proposal discussed at the meeting was approved in May 1942 by General Alan Brooke, Chief of the Imperial General Staff. Under the top secret plan Britain was to arm Vichy troops and link up with them in an Allied landing at Bordeaux and La Rochelle. At the time Britain had no official military links with Vichy and its forces were fighting Petain's troops in Madagascar.

Professor Eric Grove of the University of Salford, who discovered the papers, says he was astonished at what he found.

Image caption Alan Brooke (right) took a risk by keeping Churchill out of the loop

"My eyes widened," he says.

"Here we were having been fighting the Vichy French in Syria in 1941 and, indeed, in May 1942 we were actually fighting Vichy forces in Madagascar. And here we are talking about arming their colleagues in France itself."

What is even more shocking, in Grove's view, is the high-level backing the plan had, and not only in Britain.

"This plan has the support of the French Chief of the General Staff and General Weygand, who was a French general with a very high reputation significant support. They wanted us to arm eight French divisions to take part in the liberation of France," he says.

World War II historian Max Hastings believes that Winston Churchill, the undisputed leader of Britain's war effort, would not have taken kindly to being kept in the dark about a plan of this magnitude.

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Particularly when one of those involved in it was General Alan Brooke, the man at the very top of Britain's military machine.

"There's no doubt that one of the most fascinating aspects of this document is that the Chiefs of Staff commit to paper the fact that it's not to be mentioned to the prime minister," says Hastings.

"If he'd known what they said Brooke would have had a very, very bad half hour indeed with the prime minister, because Churchill liked to know everything."

It seems likely that both Churchill and De Gaulle were not told because of fears about what would happen if they knew.

Image caption Marshal Petain (left) and Adolf Hitler (right) in 1940

In Max Hastings' view, Churchill, "a man of passionate impulses", could have viewed the plan as iniquitous or as an opportunity.

According to Jean-Louis Cremieux-Brilhac, a senior intelligence officer with the Free French in London in 1942, De Gaulle's reaction was all too predictable.

"If we had known, it would have been something scandalous for us," he says.

But when American forces landed in Vichy-occupied North Africa in November 1942, the secret plan - which seemed to have been dropped quietly anyway - was well and truly dead.

The lack of Vichy resistance to Allied forces prompted the Germans to invade unoccupied France, and Marshal Petain's regime could no longer do deals with anyone.

But French historian and author Henry Rousso says these formerly secret papers make clear what might have happened had Vichy's General Giraud, and not General De Gaulle, taken over French forces in North Africa in 1943.

"It could have been possible that De Gaulle didn't win this political fight, and the history of France would have been, after the war, completely different. And this document reminds historians to be very cautious about the way we are writing history."

Documentwill be broadcast on Monday 19 March at 20:00 GMT on BBC Radio 4.