The story of how the post-war SAS secretly hunted down Nazis with the help of a rogue Russian prince and a Ouija board has been revealed in a new book.

It details how the organisation played a crucial role behind enemy lines during the Second World War, including carrying out 'executions in cold blood', before carrying on clandestinely despite being officially disbanded after the defeat of Nazi Germany.

A small fragment of the regiment, seen as a 'rogue unit' operating 'secretly, unofficially and possibly illegally', was financed secretly by Captain Prince Yuri Galitzine, a Russian of royal blood who worked in the War Office.

A small fragment of the SAS regiment, seen as a 'rogue unit' operating 'secretly, unofficially and possibly illegally', was financed secretly by Captain Prince Yuri Galitzine (pictured in 1970 with his then wife Princess Elizabeth), a Russian of royal blood who worked in the War Office

Insight: The story of how the post-war SAS secretly hunted down Nazis has been revealed in a new book. Lieutenant Mayne (pictured centre in Norway in 1945) led his men through the final campaigns of the war in France, the Netherlands, Belgium, Germany and Norway

It spent three years gathering evidence on Nazi war criminals and finding the graves of soldiers killed behind enemy lines, according to The Times.

The activities of the organisation, shrouded in mystery since its inception in 1941, are laid bare in the book SAS Rogue Heroes.

Author Ben Macintyre was offered unprecedented access to the SAS's wartime archive and discovered that the organisation survived a number of 'cock-ups' and interference from the upper echelons of the British Army - many who thought covert war and sabotage missions were 'not cricket'.

One of the more unconventional methods the SAS used came after the war, when the leader of the 'rogue unit', Major Eric 'Bill' Barkworth, consulted a Ouija board in a bid to find suspects. It was claimed the board helped them track down two people.

Meanwhile, the wartime archives also reveal that the SAS were the first Allied forces to discover the horrors at the Bergen-Belsen concentration camp.

Secretive: The organisation has been shrouded in mystery since its inception in 1941

Wartime archives also reveal the SAS were the first Allied forces to discover the horrors at the Bergen-Belsen concentration camp. Pictured are the survivors of the first ever SAS operation

The service's founder David Stirling (left) felt some members went too far. In the book there is a harrowing account of one of the service's leaders, Paddy Mayne, killing every German and Italian soldier who was drinking in a mess hut. One of the more unconventional methods the SAS used came when Major Eric 'Bill' Barkworth (right) consulted a Ouija board to hunt Nazis

Its men were on a reconnaissance foray in April 1945 when 'the smell hit them first' and they then discovered piles of dead bodies.

President of the SAS Regimental Association, Colonel Rupert Prichard, said he hoped the book would 'do justice to the exploits' of the soldiers and 'everything they did to pioneer the SAS'.

But he added that it was important the book had been 'based on truth rather than myth', saying: 'It had to include the bad, the ugly, the flaws, the frailties and the really impressive cock-ups that there were along with the good.'