Some of the most fascinating libraries for 18th century collections are those housed in the homes of the gentry and aristocracy. Here is one at Dunham Massey, Cheshire. See the Wikipedia article on the house here: https://en.wikipedia.org/wiki/Dunham_Massey_Hall.
I seem to recall hearing that most of these libraries are catalogued, yet I always wonder, do they contain Particular Baptist (PB) gems, always forgetting that the majority of the class of people who owned these books would never have darkened the doors of a PB meeting-house!
Michael,
If Libraries are found in National Trust Houses in the UK, they should all be catalogued on the JISC Library Hub which I believe includes all National Trust House Libraries. Whether it now includes all of them, I am not sure. So, just search and see if that rare PB book is there!
Blessings!
Julian.
PS. Whenever I see PB I think of Plymouth Brethren - our first family 'denomination'. Long since left.