More than three decades after his death, Captain Sir Basil Liddell Hart, not exactly shy of a little exposure in his day, is once again generating headlines. He could probably do without the latest batch. Files just released by MI5 to the National Archives at Kew have prompted a flurry of media reports this week. All address the same issue: did the man often regarded as Britain’s greatest military thinker of the 20th century risk blowing the biggest secret of the second world war, namely the plans for the Allied invasion of Normandy on June 6, 1944 – D-day.

“The captain who taught generals” defies easy categorisation. He was a soldier, theorist, journalist and all-round gadfly. Appalled at the awful attrition of the Somme, where he fought in 1916, he spent the interwar years badgering the British top brass about the importance of tanks and mobile warfare. In a tragic irony, Germany’s generals were quicker to spot that he was on to something, hijacking his ideas to develop the devastating tactics of the Blitzkrieg.