Thanks for your response goldy.
Oops, silly me - John Budden did of course die in 1797. I've looked at that date a gazillion times - I don't know why I typed 1789!

I have found the websites you mentioned before - yes you have got the right church! My ancestor's headstones are situated along the south facing wall of the South Chapel. According to the church website, this part of the building dates from the 14th C so would have been there long before the graves, but good lateral thinking there!
I remember visiting another church once (can't recall where) which had a grave stone up against the building - it was to honour a long-standing church sexton, but this was clearly indicated on the inscription. The inscriptions for "my lot" are very faint and covered in lichen, but I managed to decipher them all, and they all feature just names and dates. I'll see if I can dig out some of my pictures of them.
I think perhaps I should try contacting someone at the church itself. I have no idea whether churches hold that kind of information on burials - other then just a "map" of the plots. I'm not even sure who at the church I need to speak to.

I suppose what I was originally asking was - is there some kind of protocol for who can be buried in such a site right beside a church?