Many thanks for your helpful note. I have only just returned to the site, or would have thanked you sooner No information re Backwell family - my ancestor married a Mary Smithson Backhouse. She was only 14 when she gave birth to my grandfather, John Dumbell. Her husband - Samuel - was 32 years older!
My researches since suggest that there was no link with the Isle of Man before at least 1800 - unless it was via Wales. George Dumbell, founder of Dumbell's bank on the Isle of Man, was born in Flint, Wales, as no doubt you know. I have traced Samuel's ancestry back to another Lancashire Samuel who had a Welsh wife but I don't yet know which part of Wales she came from.