Thank you for your reply.
Yes, that is my parents, I have a copy of the marriage certificate and it confirms my maternal grandfathers name. With that detail I obtained the marriage certificate of my maternal grandparents from 1929, and that was revealing in that the witnesses were both relatives of the bride. The groom, James (Francis) Howarth, was a Roman Catholic but the bride, Nellie Hughes, was a protestant: the marriage took place in the RC Parish Church, but it caused a division in his family such that his father, Thomas Howarth, had little interaction with the family from that point onward.
Just before Christmas (2018) I located Thomas Howarths birth certificate which listed his mother as Ann Jane Howarth (nee Quinn). Attempts to locate certificates for that marriage or for those individuals have so far fallen on stony ground. I know that they were living at 24 Springfield, Great Bolton when James was born in 1901, at the same address for the 1911 census, and still there when James wed Nellie in 1929. Going back, the 1901 census shows Thomas and Ann living at 24 Springfield, but for the 1891 census the family appear to be living at 5 Gleave St, Little Bolton.
According to the civil registration marriage index there was a marriage in Q2 of 1884 between Thomas Howarth and Ann Jane Quinn but the GRO was unable to locate any such certificate for the given office (Bolton), volume (8c) and page (510). This has lead me to consider that there is either an error in the index or that I have misidentified the event and that that marriage included one of the other two people listed for the register page. I'm a bit stumped as to what to try next.
For the time being I'm going to enter my part of the global tree that I am confident about and continue to seek answers for the parts that I am not so confident about.