Thanks for this. It's a distinct possibility that the William Dix's baptism in 1775 is my William Bryant but, as you say, there's no evidence. A follow-on assumption could be that William took on the Bryant surname when Sarah took up with Joseph Bryant but I am guessing now. I will put a note on my tree that Sarah could be his mother but it is not more than a possibility. Oh well, I'll keep looking.
Are you researching Bedfordshire Bryants too?
Thanks again David