I´ve read the book! (probably seen the film in my early teens as well, was quite a MacLean-fan in those days, well well...)
I watched another film based on one of his books this summer, PUPPET ON A STRING starring swedish entertainer Sven-Bertil Taube as a typical eurospy-agent, pretty basic but has an breathtaking, and really looong, boatchase in Amsterdam canals, all the rest of the film is like a excuse for that...