wrote:

In our last two houses I've created bookshelves using vertical rails
into which the shelf supports are clipped (in my vernacular this
system is "Dexion", but their website doesn't seem to list this
product).

That's probably because "Dexion" it ain't! They make a whole different
system - typically free-standing 'meccano' type stuff. Spur is the most
widely known manufacturer of what you mean. Get it at B&Q,
www.screwfix.com etc. Probably the best type for your application
unless you're going to do some serioud joinery.

They make various different "attachments" which are worth browsing
through, like dividers, additional supports etc.

David