Looking up Leyburn in the Site Directory I see it is a CL (Certified Location) not a main site. Please note that no CLs are CC owned and therefore none will accept CC Site Vouchers. As previously stated, of the main sites, only CC owned sites will exchange the Vouchers, not Affiliated Sites.
If you are looking at CLs then there must be literally 100s within a 100 mile radius of Nottingham. The CC website has a reasonable search engine for CLs where you can input search criteria such as distance, toilet facilities, hook ups, etc. Unfortunately you have to ring the CLs individually for availability as they are not part of the central booking facility.