Dear Annette and Emeltom
I really appreciate your comments and information - many thanks.
I think the James Montague bur. 1787 at Stoke by Nayland could be "my" Mary's husband - the age fits perfectly. I suppose this would leave it slightly more acceptable to have children with another man - Richard Moy(se)

I wonder why they didnt marry though, as if the James, d.1787 is the right man that would have been possible.
The three other children are most interesting - I shall have to look them up and see if they offer any clues.
I suppose as you say Emeltom that Richard Moy could indeed be Richard Moy Montague - but somehow this doesnt feel right since there is an instance of a Richard Moyse being buried at Polstead in 1833.
Is there any chance of checking for more information on Richard Moy(se)? Was he also a local man and perhaps already married?
Thanks so much for your help. It is much appreciated.
Graham (in a very snowy Plymouth!)