By Jim Fish
BBC correspondent in the Netherlands
One of the enduring secrets of World War II is how German intelligence tricked the British into parachuting more than 50 Dutch agents into the hands of the Nazis.
Some classified documents have recently emerged, but historians and survivors remain bitterly divided over which side deceived the other.
A monument to the 56 Dutch agents working for the British
"A secret is a secret. The British Government will never open their books," says the elderly former agent, tapping the ash from his cigarette.
Sixty years ago in Nazi-occupied Holland, Huub Lauwers was the centrepiece of a German intelligence operation which eventually ensnared almost the entire network of Dutch agents working for the British.
On his capture in March 1942, Huub Lauwers was forced to continue transmitting as normal back to London, pretending that he was still free.
As a result of his and others' messages, more than 50 of the Special Operation Executive (SOE) agents were captured. Most of them were executed in Nazi death camps.
In the past year or so, the British Government has released more of its secret files on what the Germans called the "Englandspiel" - the game against England.
But historians remain deeply divided over whether this was merely a tragic series of blunders by the SOE, or part of an elaborate strategy of deception by London - a "double-bluff".
Using his own radio set, Huub Lauwers managed to insert coded signals into his messages back to London warning the SOE that he was in German hands. The messages appeared to fall on deaf ears.
Former agent Huub Lauwers was used to gain information for the Germans
"You begin to doubt yourself," he says. "You ask: Am I stupid or are they?"
Mr Lauwers says his SOE controllers expected most of their Dutch agents to be captured and "turned" against London.
"We were told at our training centre in Beaulieu (southern England) that we were 95% certain to be arrested.
"They told us we could transmit for the Germans, but under no circumstances should we give away our security checks (the secret signature confirming the operator's identity). I never did."
Another agent among the handful who survived was Pieter Dourlein. With a fellow agent, he managed to escape from a German prison and made his way back to England to warn the SOE against the trap.
To his dismay his controllers refused to believe his story and detained him as a suspected double agent.
After the war he was knighted for his exploits by Queen Wilhelmina, although until the end of his life he continued to believe he was the victim of British incompetence, not duplicity.
"My father thought there were a lot of amateurs in London," says his son Adrian. "My father and his fellow agents were heroes, who should not be forgotten, but in the end what was achieved? Nothing."
Historians continue to wrestle over the truth behind "Englandspiel". Many Dutch commentators suspect that London knew its agents had been turned, but was using them to convince the Germans that Holland was the focus of the Allies' invasion plans.
MRD Foot, the British historian who documented SOE's wartime operations, agrees that its handling of agents was not up to the standards of the rest of the British secret services.
British authorities received warning messages but took no notice
But he emphatically denies that the British knowingly sent the agents into a German trap as part of a deception strategy.
Perhaps the truth will never emerge. Much of SOE's wartime archives were destroyed in a mysterious fire at its Baker Street headquarters in London in 1946.
None of the key British players ever published their inside stories. As for the Dutch, perhaps the last word should go to Huub Lauwers, the last surviving agent.
He remains convinced that if he and his fellow agents were mere pawns in the "Englandspiel" it was the British, and not the Germans, who controlled the game.
"The British were playing the game for the highest stakes," he explains. "If it served to make only one section of the Allied invasion army safe, then the lives that were lost were not lost in vain."