Thanks Chris, what an amazing story. I am almost ashamed to be descended from such a miscreant.
Regarding the possibility that Mary was Mary Dear, that is interesting. My father had many tales of his great grandfather who left Newbury at quite a young age for Devonport and then Princetown (Dartmoor) for a career in what we would now call 'The Prison Service'. The name Dear rings a faint bell with me. It might very well have been something Dad told me about his great grandmother or I could be imagining things! I wonder therefore whether with all your experience you might know where the marriage records of John Mayo and Mary Dear might be found in Hampshire. A copy of certificate would be extremely useful so I would certainly like to have a go at finding one.