Unfortunately, the 1921 UK Census data will be made public in 10 years from now.
There could be records if he was a member of a pension scheme, miners’ club, working mens’ club, trades union, or church organisation.
His address would also be on marriage certificates or birth certificates of any children he had (ie your mum or dad, uncles or aunts) if any of these fall within the period around 1919.
As you mention WW I, I assume he was in the army or navy.
I'm not sure if some government institution keeps demob records for soldiers leaving the army, but a call to the Imperial War Museum could help.
BTW, if you know what regiment he was in, they usually have records going back to time immemorial.