Thanks to all who have posted information regarding my original request - lots of great and really interesting and useful information and certainly plenty I did not know ;-)) It will probably add a few more lines of enquiry to my list!!

Elfield - Thanks for that info - I believe that the Thomas Plaisted b.1856 was a direct descendent and if William b1801 is his son, then they definitely are. This would make a massive difference to my whole research.

Thanks as always to everyone for their help.
Chris