Nicola
It's tomorrow now, and I have looked at the service record for Frederick Laidler, which definitely looks like your man.He joined on 7 Aug 1917, and his occupation at the time was fitter and turner. He was 5ft 5 1/2" tall with brown hair, blue eyes and a fresh complexion. It also says he was knock-kneed!
His conduct was 'very good' and the form is stamped to show that he transferred to the RAF.
That is a summary of the main points anyway
Hope it helps
Mean_genie