Every still from a film is classed as a separate artistic work, as if they were individual photographs, and since the director died relatively recently, these stills are in copyright. I think you were assuming that. The joint owners of copyright in a film under UK law (see section 9(2)(ab)) are the producer and the principal director. Copyright lasts for seventy years from the end of the year in which the last of them dies. If the producer is still alive, copyright has many years yet to run. If you want to get permission to use the stills, you could try contacting the producer, or more likely, the production company responsible for the film. If it is still proving difficult to locate the producer and/or the production company, you could speak to DirectorsUK, which as the name suggests, is a body which represents British film directors for such things as licensing rights. They will know if there is an equivalent body which represents Italian directors.
However that might not be necessary if the point of using the stills is to enhace a point you are making in your book, as that would fall within the fair dealing exception of being for the purposes of criticism or review, provided that you also acknowledge the source of the images. However if their use is purely illustrative, in that any still would do, rather these specific ones, then I'm afraid that exception won't be applicable, and you will need to get permission.