As he was technically only a Reserve for 6 months at the end of WW1 & I don't remember anything being said about participating then would there be any records?
The Boer conflict is where I have verbal stories of participation. I also found a reference:
Telegraph battalion of Royal Engineers Signal Unit 1st & 2nd divisions
'On mobilisation both divisions were to amalgamate, and they were to be supplemented by Telegraph Reserve (GPO employees), so as to provide a HQ & 4 sections for each Army Corps.'
From The Royal Corps of Signals: History of the Corps by Cliff Lord, Chris Lord, Graham Watson et al
This suggests to me that they were a special group from the GPO that were there to support the RE rather than actually being RE. This fits in with my impressions from childhood stories that they worked behind the lines just sending out the messages rather than the engineering side.
I have no knowledge of a medal but he did receive the Imperial Service Medal in 1929, for work with the GPO & although I don't have the medal I do have the paperwork.
Perhaps I should follow this through the Post Office Museum who has records of employees & maybe this would give a clue.
Regards