Hugo it was Jack that found the military information on William and his brother Robert on the Roll of Honour. I'm a bit confused by this as Robert is still alive on the 1939 Register living at Alexander Road.
There is a William H Hughes mentioned on the Llandudno War Memorial but his mother was Laura Jane Hughes Trinity Street, Llandudno he died 16/8/1916 so he isn't the right one.
I have found William on the school register at Dyffryn Road Council School in 1907 his date of birth is 29/4/1896. Also brother Robert and sister Jennie they had come from St Clements School, Liverpool. William left school 29/4/1910, Robert left 8/12/1911 & Jennie 13/1/1909 as they were all of age. They were living at 15 Alexander Road Llandudno, father John William Hughes
There is a marriage for William Herbert Hughes in September 1922 to Eleanor Elizabeth Byatt spinster of the Parish of Eglwys Rhos. This could be him?
I have had a look at the William Hughes that Rhuddlan mentions above, but his date of birth is 3/7/1897 so we can count him out as well.
William Herbert's parents were John William Hughes born 1861 Holywell and he was a Compositor in a printing works in 1911 and Mary Grace Hughes born Llandudno 1864.