Sorry aghadowey for this late reply. I think the email prompts for these messages from you and rathmore must have gone straight to my spam folder. I need to check that.
Yes - I have tried looking for Joseph Gallagher in Irish, English (and Wales), Scottish censuses as well as "internationally" through Ancestry.com. I have been unable to find a Joseph born in the right year with a father called James who was a carpenter. There are loads of Gallaghers all over the world, it seems! Actually "carpenter" does not appear to be a common profession. But what if Joseph was not telling the truth about his father on his marriage certificate....
He married Elizabeth Hannah Mably in Reading, Berkshire in June 1918 and left the family around the time his daughter was born - well that's what we have been told.
I have also tried looking for a Joseph Gallagher b. 1887 in the 1939 census but that is so difficult because I am unsure of his profession after leaving the RAF.
I shan't give up hope - yet - though.