In the shot of the train approaching the farmer's son standing on the line, a British Railways insignia is visible on one of the coaches. This was not used until the railways were nationalised in 1948.
When Stella receives a phone call from her fiancé, she tells him that the "pips" are going and that he should insert more money to continue the call. The "pips" did not come in until 1959. Prior to that local calls were unlimited in duration and long distance calls were via the operator, who would announce when your time was up and you needed to insert further coins.
Almost all windows in during the war were taped with what looks similar to masking tape to minimize flying glass in the event of bombing. This was not evident anywhere in the film, even in scenes in Southampton (which is even shown being bombed early in the film).