He does admit, however, that being so strongly identified with one part has restricted his subsequent choice of roles. "International recognition is negative as well as positive. I know I haven't got certain parts because people have said, 'Don't be silly, we don't want him, he's Ilya Kuryakin'. But there's that old phrase: 'You buy your ticket and you take your chances'. You only have one go around. I wouldn't change a minute of the life I've had."
But just why is it that The Man from UNCLE has endured so long after the Cold War which inspired it? "It's lasted because of the chemistry between Robert Vaughn who played the other agent, Napoleon Solo and me. Also, the 1960s have an enduring charm; it was the most golden age ever. Sure, there was the Renaissance and the Middle Ages, but we had the 60s. The styles - the hair, the clothes, the music - were unique. Also, it was always very popular in America because of the agony the country went through with Vietnam. The Man from UNCLE was an escapist piece which had a Russian and an American working together for a UN-type organisation against the most ludicrous villains."
Over the years, McCallum has made several notable attempts to burst out of Kuryakin type-casting. He played a British prisoner in the memorable POW movie, The Great Escape - "for me the greatest entertainment is corn beautifully served, and that's what that film was." He also appeared as the Liverpool police chief in Hear My Song, the wonderful comedy about the singer, Josef Locke. He even starred for a couple of years in a West End run of Ray Cooney's Run for Your Wife. "That was not in the least in the Russian spy genre," McCallum laughs, "but I still had UNCLE fans at the stage door saying 'We didn't know you could do comedy'."
The UNCLE associations will be further sloughed off with McCallum's next appearance, as a child molester in Coming Home, ITV's good-looking two- part reading of the novel by Rosamunde Pilcher about two young women whose gilded lives are transformed by the onset of the Second World War. "The part was an interesting challenge," he reflects. "I was once molested as a child in a cinema. I was repulsed, but at the same time I didn't want to offend the poor man. Like some rape victims, my sense and sensibility was all about not wanting to cause a fuss. But I was interested to understand why people are like that; I wanted to bring a touch of sympathy to the man. People are often forced into things through circumstances beyond their control. That could be labelled liberal claptrap, but when you find a character like this or like Claudius in Hamlet, you try to understand him. We could still slap him in jail, but at least we'd have understood him a bit more."
Based in New York for 35 years, McCallum often returns to work here in order to reinvigorate himself. "If you live in New York, you are aware of the aesthetic side of life and of always meeting interesting people; you get into a comfortable pigeon-hole. Whenever I come to Britain, a whole other set of electrons goes into my brain and gives me a tremendous charge. Scotland in the mist in May, playing golf at Porlock, going to the Castle Hotel in Taunton and getting a gentle knock on the door at 6.30 in the morning from a maid with a cup of tea - those things are so British, they give you the best feeling in the world."
Now 65, McCallum shows no sign of slowing down. "I hope to keep working till I can't remember the lines anymore," he jokes. "I've always been a hustler. You've got to keep calling people and hassling your agent. The squeaky door gets oil. There are 90 TV channels here in the US , so there's always plenty of work. The thing is not to let the standard dip."
He is "the voice of Land Rover" in US commercials and records numerous books on tape. He has just appeared opposite David Jason in ITV's March in Windy City and starred in the US TV series, The Outer Limits and Law and Order. This week, he opened as Joe Orton's agent in an off-Broadway production about the playwright.
His next role? A transvestite father in a movie entitled Cherry about a woman determined to lose her virginity. You could hardly get further from Ilya Kuryakin than that.
'Coming Home' is on tomorrow and Mon at 8pm on ITV