The woods are full of Rhododendrons, a bush not introduced to Great Britain from the Himalayas until the late 18th century - 150 years after the Civil War.
Throughout the movie, Oliver Cromwell is referred to as Lord Protector; however, Cromwell would only become Lord Protector in 1653, whilst the events of the movie take place in 1648.
Edward Beverly's younger brother Phillip, when planning an ambush to rescue the king, refers to the riflemen he is going to station in some bushes. Rudimentary rifles had been invented but were very slow to use and not in military use at the time and civil war firearms at least in general use would be smooth bore muskets of 10 or 12 bore. Its doubtful if soldiers called rifle men would exist at the time.