If your father was not from Ireland you should repost this on a UK message board, this board is for Dublin, Ireland.
Military records are available but not sure if would cover
your father's history as I'm not sure what years are covered.
The National Archives at Kew, London has given access to their records for the British Army to a pay website - a membership is required, this and would include members of these regiments from Ireland as well. The link is on the website.
A military message board for Ireland can be found by
googling MILGENIRE, Military Genealogy Ireland.
He would of been born about 1872 if he was 18 in 1890.
The Civil Registrations of birth for Co. Down show
3 George Scott's, and 1 George Washington Scott born in Down
1864, 1867, 1869, 1869. None for Dublin.
These come with mother and father's names and mother's maiden name.
Not sure if Cumberland is the same as Cumbria but there are no George Scott births listed there. However, in all England there are hundreds listed. For 1872 there are
Hertfordshire, Northumberland, George Denton Scott, Bristol, Gloucestershire, there are many before and after
A source for England: www.freebmd.org.uk