It seems this discussion is seven years old!!
Anyway, did you ever find out more about your grandad? Bumblebee's post mentions an incident from 1922 - I believe it happened in August but only came to trial in October. Anyway, in early November, Joseph Jackson was sentenced to seven years penal servitude. Although I don't know where he served his time, it appears that this is indeed your grandad - also if your grandad was born around 1888, that would confirm it :-)