Dear Karen,
I believe that I have progressed a little further with my Winn/Stafford enquiries.
There were only 2 feasible Winn/Mary marriages in the relevant period; one a Mary Nightingale to Stephen Woon in 1797 and the second a Mary Williams to Wm. Winne in 1798. The age quoted in the 1841 Census implies Mary would be only 12 years old at this time, but I never believe 1841 ages. In fact I think that my Mary Williams was born in 1778.
Hunting through death records, I found that Stephen Woon expired long after Mary declared herself a widow when, she married Samuel Stafford.
I found that Wm. Winne who was a marine and was aboard HMS Cavalier when it was captured by the French in 1809. He died in 1810 and is buried in Essex. It would appear that Mary was a widow and not a bigamist!
I have also studied the possibility that Mr Winne & Mary may have had offspring. The only Wm. & Mary parentage I unearthed was the John Lee Winn you mentioned, but he was born more than a year after Wm. Winne died.
I am reasonably satisfied that I have found the answer to my query and your comments certainly helped.
I now need to find the dob of Wm Winne. The French record shows him as being from 'Shiffield', but so far I haven't found him in Yorkshire. The military records may be more fruitful.

Regards,

John Bennett