I also remember this PIF and have been trying to find it myself. As you say it was very evocative and reminds me of my childhood when my family would go out for drives to the countryside every Sunday. I have a feeling that the haunting music which accompanied the film may be taken from Vivaldi's - The Four Seasons. I'm sure I've heard it on one of my CD's, so I'm going to go through them this weekend and try to find it. Everything you say about the film is correct and until now I haven't met anyone who remembers it. I'm 54 years of age .
Will let you know if I find the piece of music but if you or anyone else knows where I can get hold of a copy of the PIF, please would let me know.