The only information I have on Joseph Gallagher is his marriage certificate to Elizabeth Hannah Mably and his very brief RFC record.
He was born either on 7 of March or May 1887 (poor handwriting on his RFC record).  His father was James Gallagher, a carpenter journeyman.  
There are so many Joseph Gallaghers.  I have been unable to link him with James, his father, in an Irish or UK census.
But I have now found the following birth registration on Family Search:
Name    Joseph Gallagher
Event Type    Birth
Event Date    Apr - Jun 1887
Event Place    Glenties, Ireland
Registration Quarter and Year    Apr - Jun 1887
Registration District    Glenties
Volume Number    2
Other than applying for a birth certificate, is there any way I can find out more about this Joseph Gallagher?  
Many thanks