Factual error: The revolvers carried and used by Sir Sidney Ruff-Diamond, Captain Keene and Sergeant Major Mcnutt throughout the film (and particularly at the end fight) are Webley MkVI's, not introduced into the British Army until 1915, 20 years after the film is set. Additionally, the holsters Keene and Mcnutt carry them in are webbing holsters, not introduced until well after WW1 (1914-1919).
Factual error: After finding the soldiers slaughtered at the Khyber Pass, Sergeant Major Mcnutt and Private Widdle try to see off the Burpers with a "Maxim". The Maxims in use at this time look nothing like the gun they use, which appears to be loosely based on a Gatling gun. Additionally, it's mounted on a MkIV tripod, not introduced to the British Army until 1906, 11 years after the film is set.