According to Bernard Cornwell, author of the 'Sharpe' series, he only finished half the novel in time for filming, so the beginning half of the book is followed quite accurately, but the endings are different.
The loading procedure shown is historically accurate but considered unsafe in modern times. The men are instructed to bite off the ball from the cartridge, prime the pan of their flintlock muskets, drop the butt, pour the remainder of the powder down the barrel and spit in the bullet. Priming the pan first makes the weapon ready to discharge, which is why priming the pan as the last step is considered best practice when shooting muzzle loaders. Spitting the ball into the muzzle, while fast, means bringing the shooter's head in front of his own loaded gun. Even a discharge of the powder load alone could be fatal at such a close range.
Allie Byrne is the daughter of Michael Byrne who played Major Nairn in three other Sharpe episodes.
The white gown with gold trim worn to dinner by Allie Byrne (Lady Kiely) is the same costume worn by Cécile Paoli (Lucille) in Brussels in Sharpe's Waterloo (1997).