I found the following POW information on Ancestry.co.uk that might about your Dad. I guess the best way to verify the information would be to match his service number. If you don't have it you could probably request his records from the UK National Archives:
I too was called Harry but lost the nickname when I joined the Army.
It sounds like you were named after your uncle Harold Dixon Douglas who recently died at the age of 94. I visited Inverness a few years ago, but sadly wasn't aware he was alive at the time. I'm in contact with his daughter.
Good luck with your search and let me know if I can help in any way.
The more information you can give about the people you mention, the more chance there is of someone else connecting with your family.
Dates and places of births, deaths and marriages all help to place families.
Professions also help.
'My great-grandmother mother was a Douglas from Montrose' does not give many clues to follow up! But a bit of flesh on the bones makes further research possible. But if we are told who she married, what his profession was and where the children were baptised, then we can get to work.
Maybe it is time to update the information in your profile?