I researched my grandfather's WW1 records at Kew 8 years ago. My impression at the time was that a large majority of the service records (for the army) were destroyed in an air raid in WW2. However, most (if not all) medal cards still exist which give some information on date of entry into war zones and medals awarded (I think everyone in the army would have got all or some of Pip, Squeek and Wilfred) as well as medical information. They also had war diaries.

I'm not surprised you couldn't get service records for WW1 (the odds are stacked against you) but am surprised you did't pick up any medal or medical information.