These are Grandad's discharge papers from his brief military service with the Royal Engineers in 1915.
The top two images show his Certificate of Discharge, front and back. The bottom two show his "character" — a document, common in all working trades at the time, as well as in the military, certifying that one has been a good — or in Grandad's case, "satisfactory" — employee.
It is plain from Grandad's letter, and also from family tradition, that soldiering was not Grandad's cup of tea. For an experienced miner — and Grandad was 42 years old in December 1915 — it was probably rather easy to get discharged from the service. The British government was at this point worried more about shortages of "key" workers (miners, munitions workers) than about shortages of troops.