Thank you Lady Di, this has helped enormously.
Ancestry and FindMyPast are throwing up huge amounts of incorrect hints. There are in fact at least 3, and possibly 4, William Sextons.
The 3 I've untangled with your help are:
1) My 3GG William (31 Jul 1803 - ?) from Frogmore End, Apsley, wife Elizabeth Anstee.
2) The baptist minister William (Abt. 1806 - 21 Feb 1874) from Tring. 1st wife Hannah Wright. 2nd wife Elizabeth Wright Horwood (not known if a relation to first wife, or whether she was a spinster or widower). The first baptist church in Tring was in Frogmore End. There is a road named Frogmore End (now Street) in Tring as well as in Apsley. This is the cause of a lot of confusion I think.
3) Another William born in Chesham (18 May 1804 - 11 Jun 1846) who was the son of another minister Rev. Edward Sexton. (Grave in St Mary's church Chesham) -
https://www.findagrave.com/memorial/180922588/william-sextonThere could be a fourth but I won't go there just for now lol
Paul