Bingo indeed! Thank you so much Christine once again.
With the research that you and Alan have done on my behalf I am now positive that the marriage certificate I have of John William and Isabella is the correct certificate but with the wrong details for their father's occupations and John William's father's name. Does that happen often I wonder? The final pieces of the jigsaw are the details on JW's second marriage certificate (thank you for saving me the certificate fee!) and the witnesses on their first certificate - Isabella's sister and JW's brother-in-law.
Once again I can't thank you both enough for your kindness and all the time you've taken to help me out. I can now go farther back with confidence ..... until I hit the next brick wall, but again, you've both taught me a lot about researching and thinking laterally.
Andy