An MI5 "bungle" which emerged during Covid sensationally revealed that Winston Churchill was in on the Valkyrie plot to kill Hitler, according to a leading historian.
The spooks dumped piles of top secret wartime files on the internet during pandemic lockdowns covering the attempt by Colonel Claus von Stauffenberg to blow up the dictator.
But Security Service weeders charged with sifting out sensitive documents belonging to sister spy agency MI6 missed the ones which contained the 78 year old bombshell secret.
Now MI6 chief Richard Moore - known as C - is being pressed to come clean over the Secret Intelligence Service’s part in the 20 July 1944 attempt on Hitler’s life so historians can put the record straight.
The UK has always denied being involved in the plot which featured in the 2008 Tom Cruise movie Valkyrie insisting it was solely the work of disaffected German officers.
But one of the plotters managed to get away. He was the 45 year old Lufthansa lawyer Otto John who squirrelled his way out of Berlin on the flight deck of one of his airliners bound for Madrid four days after the explosion.
He made his way to Portugal and was exfiltrated from capital Lisbon by MI6 and whisked to Britain.
What the files accidentally reveal is that he had been recruited as an agent by MI6 two years before the attempt on Hitler’s life under the codename Whisky. And met his handlers 12 times in the lead up to the blast.
Britain’s top espionage expert, the former Tory MP Rupert Allason who writes under the name Nigel West, said: “This is of enormous historical importance.
“It means John was a British SIS agent and no mere plotter. It also means emphatically that Churchill knew about the plot and gave it his approval.”
Churchill was briefed daily during the war by No 10’s SIS liaison Major - later Sir - Desmond Morton.
Mr Allason said: “It is inconceivable that something of this magnitude was not discussed at those meetings. And to go ahead it would have needed the the PM’s political sanction.
“History must now be rewritten. That is why I have approached C to ask him to release other files to put all this into context.
“Richard Moore says he wants more openness and transparency in his service and this would be the perfect way to prove he means it.”
Stauffenberg planted a suitcase bomb in Hitler’s Wolf’s Lair HQ in east Prussia. The deadly plan went wrong when the case was moved behind a thick table leg which shielded Hitler from the blast.
The explosion killed four people but the Nazi dictator escaped with just a perforated eardrum and his trousers burned and shredded.
Witnesses said Hitler was more concerned about his ruined trews than the officers who had died.
Had von Stauffenberg’s assassination plot succeeded he planned a miliary coup to take over Germany, restore the monarchy, and end the war by making peace with the Allies.
British-made explosives and triggers were used but at the time they were believed to have come from a cache dropped to Special Operations Executive saboteurs and captured by the Germans.
John’s role as the intermediary between the plotters and British spymasters was contained in declassified MI5 files which had lain unread in the National Archives since 2007.
The foreign spy agency MI6 does not release its secret files to National Archives so the identities of agents is protected even after they are dead. John does not even appear in the SIS official history.
When Covid struck the Public Records Office in Kew, west London which holds the archives pulled down the shutters and put files which previously cost £3.50 each to download on the internet for free.
Mr Allason said: “The cost of downloading thousands of files is prohibitive but being able to do so without paying was a boon to researchers.
“I had nothing to do during Covid so I began going through them. That’s when I made this extraordinary discovery.
“The hairs on the back of my neck stood on end when I found this because it was so momentous.”
The revelation is now detailed in the new book Hitler’s Trojan Horse by Nigel West.
He added: “At the time SIS did not use letterheads for their correspondence so their documents were released with the MI5 files when they shouldn’t have been.
“You have to know what you are looking for to spot them. And that’s why the weeders missed them.”
One document confirms that John was “an SIS agent for two years and whom the Germans are hotly pursuing on the footing that he was party to the attempt on Hitler’s life.”
It was written by senior MI5 officer Herbert Hart who was in charge of the Ultra decrypts masterminded by computer wizard Alan Turing at Bletchley Park’s secret listening post.
It took months of preparation to get the bomb inside the conference room where Hitler was meeting with aides. Once placed Stauffenberg made an excuse to leave the room.
But after the failed attempt Stauffenberg and other conspirators were quickly rounded up and shot in the courtyard of the Bendlerblock, the army HQ in Berlin. Others were hanged with piano wire in the Gestapo’s Ploetzensee prison.
Cruise wears an eye patch to play von Stauffenberg in the Valkyrie movie. In 1941 the colonel lost his left eye, right hand, and two fingers on his left hand while fighting for the Afrika Korps in Tunisia.
The Nazis discovered John’s involvement in the plot after he fled to Spain and executed his Berlin University law professor brother, Hans, instead.
One top secret report from the bundles MI5 released says: “John has always been anti-Nazi. He and his brother had parted ways with many of their schoolmates and later from their student friends on this matter.”
Hans John was not the only innocent victim in the plot’s fallout. The Gestapo executed 5,000 people of the 7,000 they arrested.
John continued working for British intelligence interrogating captured German spies and playing a key role in the Political Warfare Executive which broadcast propaganda to a collapsing Germany.
But Mr Allason suspects there was another reason John’s MI6 activities had to be kept quiet. Six years after the 20 July plot John became head of the West German counter-intelligence service BfV, their equivalent of MI5.
Mr Allason added: “That meant an MI6 asset was in charge of a European spy agency on the frontline of the Cold War.
“The intelligence he could have provided to the British without West Germany’s knowledge would have been priceless.”
But after a ceremony on 20 July 1954 to commemorate the 10th anniversary of the Valkyrie plot John disappeared and turned up in East Germany three days later. The West Germans thought he had defected.
But he ended up in the hands of the Soviet KGB and for the next 18 months spoke out against the West from his new East German home before slipping back into West Berlin where he was immediately arrested.
He protested that the KGB had kidnapped him but was sentenced to four years jail for treason. He complained that the judges who convicted him were former Nazis bent on revenge.
John died in an Innsbruck sanitorium in 1997 after years of trying to prove his innocence. He claimed his statements against the West were made only to ensure his safety in the East.
A fifth and final attempt to get the case reopened a year before his death was turned down by a German court.
The British were unable to help because to do so would have meant admitting that MI6 had been running John all along.
Even East German spymaster Markus Wolf - the model for spy novelist John Le Carre’s cunning Karla - said John had been drugged and abducted to the East in a KGB op. But what really happened remains one of the enduring mysteries of the Cold War.
Mr Allason said: “In my view John had some kind of breakdown at that ceremony.
“Germans were not keen to celebrate the plot and still regarded it as treachery against the Führer.
“That was too much for John to cope with after everything he had been through.”