Hello Mousey,
I haven't found very much at all, I am afraid. I think that William F. Sebburn 1918 was illeg son of Martha Margaret 1891. She was dau of Thomas Sebburn (Seabourne) and Elizabeth nee Richards. (censuses)
In 1911 Martha was still with her parents in Llangeinor,Nantymole,Glamorganshire,Wales (familysearch)
I need to get William's birth and marriage certs to prove this but funds are a bit tight at the moment and family history expenses must wait.
All I really have as proof at the moment is the freebmd ref
Births Dec 1918 Sebburn William F Sebburn Bridgend 11a 1579
If you have other info that can prove our William's are the same, that would be great.
Yours
Vic