John le Carré has warned that the intelligence services could "become as much of a peril to our democracy as their supposed enemies" if they are not subjected to rigorous examination. The novelist was defending himself against the accusation that his former colleague John Bingham, upon whom he based his most famous creation, the spy George Smiley, "deplore[d]" how his novels revealed the "secret world" of the intelligence services.

Writing under his real name David Cornwell in a letter in Wednesday's Telegraph, the author and former MI5 and MI6 agent acknowledged the debt he owed his mentor Bingham, a man for whom he "shall always have unqualified admiration". But the novelist also gave a robust defence to the claim in Tuesday's Telegraph from Lord Lexden that Bingham "was not treated as respectfully as he deserved by his protégé, John le Carré", that Bingham was "hurt by the portrayal of his secret world in the novels", and that Bingham once said that le Carré "was my friend, but I deplore and hate everything he has done and said against the intelligence services".

John le Carré believes 'our secret services could in certain circumstances become as much of a peril to our democracy as their supposed enemies'. Photograph: Jane Bown

Le Carré, however, said that "where Bingham believed that uncritical love of the intelligence services was synonymous with love of country, I came to believe that such love should be examined. And that, without such vigilance, our secret services could in certain circumstances become as much of a peril to our democracy as their supposed enemies".

"John Bingham may indeed have detested this notion," wrote the novelist. "I equally detest the notion that our spies are uniformly immaculate, omniscient and beyond the vulgar criticism of those who not only pay for their existence, but on occasion are taken to war on the strength of concocted intelligence."

Bingham has been in the headlines for the past week after newly released files revealed how, during the second world war, he tricked British Nazi sympathisers into believing he worked for the Gestapo in order to obtain their secrets.

George Smiley was played by Gary Oldman in the recent adaptation of Tinker, Tailor, Soldier, Spy.

He has long been acknowledged by le Carré as part of the inspiration for his genius spymaster Smiley, whom he describes in 1974's Tinker, Tailor, Soldier, Spy as "small, podgy and at best middle-aged, he was by appearance one of London's meek who do not inherit the earth".

"Surely there can be few better tributes to a friend and colleague than to create – if only from some of his parts – a fictional character, George Smiley, who has given pleasure and food for thought to an admiring public," wrote le Carré on Wednesday. "He was a most honourable, patriotic and gifted man, and we had wonderful times together."

But the novelist was well aware of the animosity with which the late Bingham viewed him. In an introduction to one of Bingham's own crime novels, 1952's My Name is Michael Sibley, he wrote that "if John had been able to hate anyone for long, he would have hated me", and "that we had been friends and colleagues only added spleen".

"John had been my professional mentor. He had been one of two men who had gone into the making of my character George Smiley. Nobody who knows John and the work he was doing could have missed the description of Smiley in my first novel, Call for the Dead. 'Short, fat and of a quiet disposition, he appeared to spend a lot of money on really bad clothes'" wrote le Carré in 2000.

As far as Bingham was concerned, wrote le Carré in the introduction, he was "a literary defector who had dragged the good name of the service through the mud", who had "supped at King Arthur's table, then sawn its legs off", and it was "no good my protesting I was engaged in a literary conceit".

Bingham died in 1988. In his introduction to My Name is Michael Sibley, le Carré called him "an extremely gifted and perhaps under-regarded British crime novelist", and asked readers "in my sadness, and love of John … to do him justice, not just as a British patriot and supremely able intelligence officer, but as an intuitive scholar of human motive, which is what informed the writer in him".