British intelligence agency MI6 obtained vital secrets from a spy operating at the very heart of Hitler’s high command during the most crucial years of the war, newly discovered documents reported in The Times of London on Saturday show.

The secret agent, code-named "Knopf," furnished the intelligence service with information on Hitler’s plans in the Mediterranean and on the Eastern Front, the health of Field Marshal Erwin Rommel and even the location of the "Wolf’s Lair," the Fuhrer’s headquarters in eastern Prussia.

Historians tended to play down the wartime role of MI6, but the discovery of Agent Knopf by the Cambridge historian Paul Winter shows that Britain obtained accurate and highly valuable intelligence from a network of agents in the upper ranks of the Third Reich.

The documents, uncovered in the Churchill Archives in Cambridge and the National Archives, show that Knopf and his sub-agents alerted British Intelligence to German plans for an invasion of Malta in 1942.

They also relayed Rommel’s intentions in North Africa and revealed Hitler’s fatal obsession with capturing Stalingrad on the Eastern Front.

The Fuhrer was "determined to capture Stalingrad at all costs," Knopf reported. Hitler’s disastrous assault on the Russian city, which led to the destruction of the German 6th Army, is seen as a turning point in the war.

Agent Knopf was initially recruited and run by Polish Intelligence. In 1940, the Polish government, in exile in London, agreed to hand over all its intelligence material to MI6, providing Britain with a steady stream of top-grade intelligence for the rest of the war.

The archives of MI6 remain closed and the real identity of Agent Knopf may never be known — but the newly uncovered documents indicate that the star spy was a German with access to high-grade military information.

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