The British establishment is not only a perfect machine for producing secrets and lies.
It also produces the mavericks and misfits who thrive in the secret world.
Establishment types seem to come in two varieties: smooth conformists who do everything by the rules, and mavericks who break every rule but are nevertheless tolerated because they are members of the club.
The first type is sent into the Foreign Office and the second into MI6.
The best spy novels are like distorting mirrors in fairgrounds: by exaggerating this or that feature of Establishment Man, they allow the reader to understand the ideal form.
The other great theme in British spy novels is geopolitical decline.
How can people who were “trained to Empire, trained to rule the waves”, as one of Mr le Carre's characters puts it, bear to live in a world in which the waves are ruled by other powers and statecraft is reduced to providing fuel for the welfare state?
Fleming's novels are full of laments about Britain's “crumbling empire” and its dependency-producing state.
“You have not only lost a great empire,” Tiger Tanaka, a Japanese spy, tells Bond, “you have seemed almost anxious to throw it away with both hands.”
Mr le Carre once described Britain as a country where “failed socialism is being replaced by failed capitalism”.
The Circus, as he called the secret service's headquarters, is a physical manifestation of decline: cramped, shoddy, reeking of rising damp, just one hasty repair away from collapse.
Why remain loyal to a country that has made such a mess of things and to an establishment soaked in hypocrisy?
Mr le Carre's traitors (like the Cambridge spies who inspired them) betray their country not for money but because they have transferred their patriotism to the Soviet Union.
But what makes Britain's best spy novels so good is that they toy with disillusionment only to reject it.
For all its faults, they say, Britain is the best of a bad lot.
Bond is so besotted with his country that he boasts that “British food is the best in the world”.
For all his professed Europeanness in the new novel, Smiley is the model of a British gentleman.
And spying provides Britain with a way of reclaiming its greatness, by excelling in the most sophisticated form of foreign policy.
The Americans have the money and the bluster, but the British have the brains to spend it wisely and restrain the Americans from going over the top.
Felix Leiter, Bond's opposite number in the CIA, admits that Bond is playing “in a bigger league” than he is.
Smiley is more subtle than his “cousins” in America.
The secret at the heart of the British spy novel is that Britain is much better than it seems.
The writers agonise over decline and hypocrisy, only to conclude that the British are cleverer and more civilised than anybody else.
A comforting illusion wrapped in a tale of disillusionment: you can't get more British than that.