...Robert Holmes agrees that the Russian government was not involved at an official level but believes events on Cuba, being marked this week, and those of a year later are intimately related. A former diplomat, who served in the British embassy in Moscow between 1961-2, he has made a fresh study of that fraught era. His conclusion is neither as neat as Bugliosi’s “lone nut” hypothesis nor as labyrinthine as the conspiracies proposed by authors like Jim Marrs, whose work inspired the Oliver Stone film JFK.

Oswald may have acted alone, thinks Holmes, but he was almost certainly under the control of an outside force. In his new book, A Spy Like No Other, he suggests that Kennedy was most likely the victim of a rogue element within the KGB, hardline Stalinists who were, by training and temperament, incapable of taking the humiliation of Cuba lying down. They conspired behind the back of Nikita Khrushchev, the Soviet premier, to take revenge on Kennedy, whose cool but resolute stance, bolstered by overwhelming US superiority in missiles and bombers, had forced the withdrawal of Russian medium-range nuclear missiles from Fidel Castro’s Cuba.

“Cuba was a humiliation of the first order for these men,” says Holmes. “They believed in the Stalinist way of doing things: hit your enemy, and hit hard....