You can find service details of WW1 service people on the national archives sight, this includes individual service records (they are so old as to be outside the Privacy Act constraints).
If you find details of the people you are interested the NA will supply copies, beware though it can be quite confronting to find very stark records of fallen family members.
Unfortunatly there is a lot missing from this period as the storage building was hit in the blitz during round 2.