In the scene at the golf course, the policeman keeps blowing his whistle as he chases after the suffragettes. In reality police whistles were used on city streets to call for back up from other officers nearby in the event of an incident. Since the policeman in this case was assigned as a lone protection officer to a government minister who was out playing golf on a windswept rural golf course, there would have been absolutely no benefit in blowing a whistle whilst he gave chase. Indeed it would have hampered his pursuit.
When Christopher is talking to his brother in the carriage before the wedding and they are arguing about whether Christopher's mother was from Yorkshire, his brother says "Oh, South Riding by a whisker." Yorkshire (historically) was divided into three ridings (or thirds): North, East, and West. There was no South Riding.
When Christopher and Sylvia first meet on the train, he uses a Zippo lighter to light her cigarette. The Zippo was not invented until 1932, and not in production until 1933, some 25 years after this scene takes place.