Approximately how many soldiers were court-martialed in WWI? Specifically the British Army?

There were quite a few and many were shot by firing squad. I believe the youngest was a fifteen year old who gave a false age on enlisting. It is also said that officers were never court marshalled for cowardice, this is because they were reduced to the ranks prior to being tried.

I would be surprised if the number was more than 100 since the Germans executed only 48 soldiers during all of World War I (compared to 12,000-15,000 in World War II). The U.S. did not execute anyone in World War I and only one (Eddie Slovik) in World War II. The French executed a small number during the mutinies which occur ed after disastrous attacks in World War I and few if any in the Second World War.