Thanks Leslam, yes, I had tried all the by-ways and side-tracks, but still nothing. And yes, I saw Maria, but no, def. not her. But thank you so much for your offer of taking a look.
I have actually now had the benefit of a trip up to Birmingham, and a visit to the Archives (thank goodness I made it before they close until September next year!!!). And looking at the film for St Thomas burials, it is clear that my assessment from trawling through Family Search was accurate. There is literally just one burial noted for St Thomas in 1857. The records go from December 1856 straight to January 1857, with just the one exception! And I checked the page numbers, and they are consecutive.
Unfortunately, I had a lot to cover and was working to a deadline, and the facilities were not very good, so I did not have the opportunity of following this up with Library staff. But I will do this next year, when everything is functioning again.
Jane