I've just watched this movie--it was screened at lunchtime on C4 last week.
The Imdb database just says "Shepperton Studios" with no statement of where the town really was. A subsequent discussion on that website suggests the town was possibly Shepperton itself or Laleham.
Well, the station featured had "Southern Railway" on the nameboard--which is anachronistic;if it said anything, it would've been Southern Region in 1957--and it can't have been Shepperton Station as Shepperton is all on the level. (The station in the film was in a cutting.) Laleham has no station. But that doesn't mean a combination of scenes wasn't used with stock footage of a station.
Although I have driven through the area, I don't know it at all. But the church at the end is on the outside curve of a right-angled bend of a road. The churches in Shepperton and Laleham are all beside straight roads, according to my A-Z of Surrey. There are other town shots in the film but there are no distinctive (to me) features.
So, if it wasn't Shepperton or Laleham, where could the town have been? It could've been any town in the South East! But I deduce that some people who post here are ex-film crew, so perhaps somebody knows..........