Hi David,
Thanks very much for all of your effort. It is good to know the church in which they married, and although the entry doesn't really shed any light on the parish where they would have been born or baptised, it is still useful. I have found the baptism for Dinah in Bristol, so I am supposing that where it states both of this parish, they may have just been living there at the time of the marriage.
Thanks also for the info about Bedminster, I had only seen on a map that it was in close proximity to Bristol, so that clears up that confusion.
I will note the baptisms you found for William Dyer's, hopefully one of them could be the one! I have widened my search outside of Bath, but of course there is no way of knowing which if any other parishes could be correct.
Thanks again,
Kelly.