Thank you to Orielbenfro for your reply.
It is impossible to believe this is not the correct marriage, especially connecting the same date!
The fact that both parties were widows means that Thomas would be the married name of Ann - always one step forward and another back! John Elliott didn't have much luck with wifes, as Anne died in 1843, and thereafter John re-married again (to Jane James in 1847).
William and Mary had two siblings,one of which was Sarah, who's baptism in 1834 in St Martins is recorded on IGI, so not sure where that takes me on the non-conformist suggestion, but may still be worth a look. Mary was my 3 x gt grandmother, so I am quite keen to fill in the details.
Regards and thanks for the lead
bluegenes