His was a hidden life, of outward conformity and inner rebellion. In retrospect, he would feel that he had been schooled into becoming a spy, learning the enemy’s language, wearing his clothes, aping his opinions and pretending to share his prejudices. Like Graham Greene, he learned to live a secret life, and would later liken his boyhood to living in occupied territory.

This was a period of extraordinary reversals, when former foes became friends, and former friends foes. The Germans, against whom the British had poured out all their strength only a few years previously, had been co-opted into the Cold War against Communism; while the Russians, who had done so much to slay the Nazi monster, had become adversaries in a worldwide ideological struggle. This turnaround had occurred with shocking rapidity. The same pilots who had bombed Berlin in 1945 were running the Berlin airlift in 1948.

MI5 was not a very impressive organisation. ‘For a while you wondered whether the fools were really pretending to be fools, as some kind of deception,’ David wrote later; ‘but alas, the reality was the mediocrity. Ex-colonial policemen mingling with failed academics, failed lawyers, failed missionaries and failed debutantes gave our canteen the amorphous quality of an Old School outing on the Orient Express. Everyone seemed to smell of failure.’

MI5 encouraged a level of secrecy that bordered on the absurd. New recruits curious about the identity of their mysterious employers were fobbed off – ‘just the War Office, old boy’. A desk officer who shared an office with David had been at Leconfield House some weeks before David informed him, over coffee one morning, that he was working for MI5.

MI5 operates on home territory, which in those days included the colonies of the British Empire. The function of MI6, on the other hand, is to collect secret intelligence and mount covert operations overseas. Another way of looking at the difference between the two organisations is that MI5 is essentially defensive, whereas MI6 is offensive.

Britain had only reluctantly supported America in endorsing and promoting German rearmament, which remained a controversial issue at home. Though officially committed to the goals of the Federal Republic, the British were nervous of any prospect of German reunification. ‘I love Germany so much that I would like three or four Germanies,’ quipped one British diplomat.

If David deplored the lack of interest his own countrymen showed in the tragedy unfolding in Indochina, he was still more critical of American interference in the region. As Graham Greene had done a generation before, he blamed American meddling for the developing disasters. In his notebook he poured out his loathing of the CIA men he had encountered: ‘I hate them more than I hate myself, more than I hate a hangover. They’re the one bunch I hate morally: I only have to see their Mormon haircuts and listen to their open-plan charm. I have only to hear them call Europe “Yurrp” and I start sweating at the joints.’ While staying at one of the Bangkok hotels he expressed his disgust at being served ‘one of those ghastly American sandwiches, full of wooden spikes’.

Updike bracketed le Carré with Tom Clancy, Robert Ludlum and Frederick Forsyth, as authors of Cold War thrillers read on aeroplanes by men in business suits – ‘rather, in business trousers, with their jackets nicely folded in the overhead rack and their neckties loosened away from their shirt collars an artful inch’.

When Hare had suggested that David’s increasing engagement with politics was in the ‘great tradition of writers becoming radicalised in later years’, David responded by citing the German term Alterszorn – ‘the rage of age’. He recognised the danger that he might lose readers if his books became too polemical. ‘Story and character must come first,’ he said. ‘But I am now so angry that I have to exercise a good deal of restraint in order to produce a readable book.’