Jeanette,
Without all his record, it's going to be a mixture of guesswork and supposition.
10/11/17 Clearing Office RGA Dover. (27 S B)
The most likely reason that he returned to the UK is that he was sick or wounded. My guess is that this may be the initial onset of the Nephritis that eventually led to his discharge under Para 392 (xvi). The Clearing Office is probably the equivalent of "on the strength of the Depot", often used to mean inactive due to hospitalisation, convalescance etc.
Following this period (up to 3/3/18) he may only have been fit enough for Home Service, hence he was initially posted to the Plymouth Garrison and later to Cork. It is also more than co-incidence that the war diary for 27 Siege Battery seems to end in February 1918. Did it return to the UK and take up coastal defence duties?
I'm afraid it's more of a scenario than hard fact.
Phil
