Just north of West Wycombe between there and Saunderton, West Wycombe Hill is to the right background, there is a foot crossing in the right foreground from which this image (and that of 50xx) was captured. In the summer of 1960 train reporting number M20 was the 16.10 Paddington to Birkenhead.
Loco may be No. 6019. map reference 483267,195555.