Now that I finally have details of Thomas's 1874 marriage, I know that his father was John Alcock, deceased, Tailor. It was an RC marriage in Preston, Lancaster County.
So far I have been unable to track John Alcock. Thomas was born in Hanley, Staffordshire, but lived in Preston. The only possible John Alcock from the 1851 census was a cordwainer (the others were publicans or bricklayers), which is loosely associated with sewing perhaps, albeit shoes. However his son Thomas was born in Leigh, Staffordshire, which looks to be not very close to Hanley which was the birthplace of my Thomas.
Any help gratefully received.
(Not sure if I should be posting this in Staffordshire or Lancashire!)