The officer's medals are worn in the wrong order and he could not possibly have been awarded a victory medal at the time of the action. It was awarded in 1919.
The British Officer shown early in the film ordering the attack is wearing the three WWI medals "Pip, Squeak and Wilfred" which were issued in the 1920s.
Sgt Major Wilkins looks at his watch several times during the film, the watch is of a much more modern style than found at the time and it is also a quartz movement as is evident by the the ticking of the second hand which jumps one second intervals instead of a steady sweeping movement made by mechanical movements.
In the final scene, he places roses on her grave, but he's wearing a very modern looking watch with metal strap.
During the trench scene prior to going over the top, there is a modern pallet stood in the trench - this type was only made after the 1950's and much more commonly from the 1970's.