That longtime product of Leeds, Monopoly, continues to be a perennial favourite – but during Britain's darkest hour, it was far from just a game.

A wartime plan hatched between the government and John Waddington's, who then manufactured the boards and players' tokens in Wakefield Road, Stourton, saw secret escape maps produced by the company for Allied prisoners of war.

In an especially cunning plan, Monopoly boards were used by fake charities to send the maps and related messages to prison camps in Nazi-occupied Europe. Equipped with the information, numbers of shot-down pilots and other captured servicemen managed to break out and some made their way to neutral countries and back home.

The system was set in place by MI9, a secret government department responsible for helping prisoners of war and liaising with resistance movements in continental Europe. Section Nine of the British Directorate of Military Intelligence in the War Office, to give it its full name, carried out trials of maps printed by Waddingtons on silk, rayon and tissue paper as early as 1940.

Hiding places included cigarette packets and the hollow heels of flying boots, where the flimsy maps did not rustle suspiciously and, in the case of those printed on cloth or mulberry leaf paper, could survive wear and tear and even immersion in water if an aircraft 'ditched' in the sea.

Debbie Hall, formerly of the British Library and now at the Bodleian Library in Oxford, has studied the secret history of the silk maps, and the involvement of the famous Yorkshire firm. She says:

In December 1939, MI9, the branch of the secret service responsible for escape and evasion, was set up. It was made clear that it was the duty of all those captured to escape if possible. One man who was behind many of MI9's most ingenious plans, including the Waddington project, was Christopher Clayton Hutton.

Stalag Luft III prisoner of war camp for captured airman; one of the destinations of Monopoly maps. Photograph: Hulton Archive/Getty Images

Waddingtons already had the technology to print on cloth and made a variety of board games, packs of cards and the like that could be sent to the camps. They began by printing silk maps for supply to air crews, British and later American, and went on to conceal maps inside Monopoly boards, chess sets and packs of cards which could be sent into the prison camps.

Prisoners of war were allowed to receive parcels from their families and from relief organisations such as the Red Cross. The spooks did not want to compromise the latter and so set up a range of fictitious charitable organisations, often based at fake addresses or bombed buildings, to send games, warm clothing and other small comforts to the prisoners.

One of the major problems of captivity was boredom and games and entertainments were permitted as the guards recognised that if the prisoners were allowed some diversions they would be less troublesome. Once several Monopoly boards had got safely through, MI9 and Waddingtons developed a code to show which map was hidden in the set.

A special code was even used to indicate to the ministry which map was concealed inside a particular game so that it would be sent to a prisoner of war camp in the appropriate area. Hall says:

A full stop after Marylebone Station, for instance, meant Italy; a stop after Mayfair meant Norway, Sweden and Germany, and one after Free Parking meant Northern France, Germany and its frontiers. "Straight" boards were marked "Patent applied for" with a full stop.

Present day North Yorkshire county councillor John Watson, from Wetherby, whose father Norman Watson was instrumental in turning Waddingtons into a household name, says:

My father was fond of telling tales about Waddingtons part in the war effort. The silk maps were a major feature of such recollections. As I remember it, some of them were used as part of airmen's uniforms. I also know that the silk had to be specially treated so that it wouldn't distort through environmental pressures or through time. The Monopoly ones were laminated within the boards. He also said that several Monopoly sets were sent out containing tokens made of pure gold to be used by prisoners to pay for assistance with their escapes. One other tale was that, once it was discovered the German guards were not searching the Monopoly sets themselves, real German currency was included in some of the packs of Monopoly banknotes.

These things may just have been exaggerations on my father's part but I doubt it. He was genuinely proud of the company's role during the war and I don't think that he would have needed to embroider the truth.

Another researcher into the subject is Barbara Bond, a graduate of Leeds University and former civilian researcher at the Ministry of Defence who is now pro-chancellor of Plymouth University and past president of the British Cartographic Society. She says:

MI9's philosophy of "escape-mindedness" was instilled into the members of all three services and the practical application of that philosophy was seen in the production of escape kits and aids to escape such as maps. Initially the escape kits were in the form of small cigarette tins which contained concentrated food, tape, thread, tiny saws and compasses. The methods of getting the maps through to the prisoners of war were very ingenious. They were hidden in playing cards, pens, pencils, gramophone records, and game boards. It was a cardinal rule in MI9 that they never used Red Cross parcels. Instead they set up their own cover organisations such as the "Prisoners' Leisure Hours Fund" and the "Licensed Victuallers' Sports Association". These dispatched both ordinary parcels containing clothes and the special ones containing escape aids.

You can read more in the excellent The Waddingtons Story by Victor Watson, John Watson's brother and former head of the firm who famously saw off a predatory corporate raid by Robert Maxwell. It is published by Jeremy Mills Publishing.