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In the run-up to D-Day, a French soldier exiled in London was given the task of telling his compatriots how they should react once the liberation of their country began.

On 31 May 1944 Jean-Louis Cremieux-Brilhac sat in his study at 17 Hill Street Mayfair, and typed out the D-Day orders for the people of France.

These were the instructions to be read over the French service of the BBC, telling the population how to react once they learned the Allies had landed.

The document - four pages of flimsy paper marked "secret", type-written with annotations in pencil - has been in Cremieux-Brilhac's possession ever since.

Now aged 97 and living in Paris, he recalls with perfect clarity the excitement of the time.

"I was secretary of the Free French Propaganda Committee. There were five or six of us, and my job was to draw up the D-Day orders taking account of our discussions earlier in the day.

"We knew that the invasion was coming but of course we did not know exactly when. We had to be ready."

The instructions were intended "for all French men and women not organised in, or attached to, a Resistance group".

Image caption These instructions, to be released on "J" Day, tell French men who are in organised groups or attached to resistance units to escape in order to form the units of the FFI - French Forces of the Interior - and calls on those who aren't near postings to head for the countryside

Quite separate orders were broadcast to members of the Maquis. These were the famous "personal messages" read out on the BBC - often lines of French poetry that carried coded information about targets to attack.

But that was not part of Cremieux-Brilhac's remit, which focused on the population as a whole.

"The main message we sent was to put France in a state of general alert. And then there were specific instructions for particular sectors of the population - like town mayors, police, factory workers and so on," he recalls.

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In fact there had been heated discussion in the propaganda committee about how far to incite the French into acts of opposition to the Germans.

The Communist party - which was extremely influential in the Resistance - wanted a immediate general insurrection on D-Day, with workers going on strike and calls to arms across the country.

Cremieux-Brilhac was part of the majority that resisted this idea.

"It would have been a very stupid mistake. The Germans would have taken massive reprisals - as indeed they did at places like Oradour-sur-Glane (a village where hundreds of civilians were massacred on 10 June)," he says.

"The policy we decided on was of a gradual, phased insurrection, developing in accordance with the advance of Allied forces. In the end this is exactly what happened."

Nonetheless his document states unequivocally that from D-Day on, "all French must consider themselves as engaged in the total war against the invader in order to liberate their homeland.

"It is not a question of choosing to fight or not to fight; or when to fight. They are all soldiers under orders."

"Every Frenchman who is not, or not yet, a fighter must consider himself an auxiliary to the fighters.

"However," it goes on, "it is important that there not be - under the pretext of providing assistance - a disorganised rush to join the Resistance which would have the effect of leaving it paralysed.

D-Day 70 Watch coverage of the commemorations of the 70th anniversary of D-Day Details of the BBC coverage of D-Day's 70th anniversary

"Only those men and women should join the Resistance who are already armed and have been asked to do so by official representatives."

Cremieux-Brilhac had particular instructions for people living inside the combat zone, ie Normandy.

They were told to "disrupt using all means transport, transmissions and communications of the Germans".

Interestingly a line that reads "Cut telephone and telegraph lines" has been crossed out - presumably because this was regarded as the job of the Resistance.

The people of Normandy are told that "every minute lost to the Germans is a minute gained by the Allies. A car stuck on the road can delay traffic for 10 minutes - and blocking an enemy transport for 10 minutes may ensure the success of an Allied operation."

Conversely the population is urged to do everything to help the Allies, for example "serving as guides to their troops and parachutists; and locating and signalling traps and minefields".

In 1944 Cremieux-Brilhac was a 25-year-old student-turned-soldier - with already an exciting adventure behind him.

Image caption Cremieux-Brilhac (far left) with fellow soldiers

To think it was me personally who wrote the general guidance for D-day for the whole French population. It is remarkable Cremieux-Brilhac

In 1940 he had been captured in France by the advancing Germans and sent to a POW camp. He escaped and made it to Russia, but there he suffered more internment (worse, he says, than under the Germans) because this was still the time of the Nazi-Soviet pact.

Eventually when Germany invaded Russia in 1941, Cremieux-Brilhac was released and along with more than 100 other French soldiers taken by Canadian ship from the Arctic port of Archangel to Glasgow.

The next day they arrived by train at Euston station in London. There is archive newsreel footage of the party being welcomed by a Free French officer.

Cremieux-Brilhac is sadly not identifiable in the crowd, but he does recognise several of his former comrades.

Looking back on D-Day, Cremieux-Brilhac remembers the "waves of planes flying over London. There were hundreds of them. It was so impressive. We Free French had no doubt that the landings would succeed."

"It was such a huge privilege for a young soldier like me - just a student really - to have been so close to the heart of decision-making. I knew De Gaulle and all the resistance leaders.

"And then to think it was me personally who wrote the general guidance for D-Day for the whole French population. It is remarkable."

His secret document he promises to bequeath to the French National Archive.

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