
There are breeds that have fewer registrations than that, Foxhound 14, Skye Terriers only had one more with 37, but many are not British breeds, my own breed around in the UK since 1870's is down to under a 100.
Established breeds with lower registrations than the Glens, Finnish Spitz 35, Hamiltonstovare 18, Ibizan hound 7, Pharaoh Hound 9, Maremma Sheepdog 9, Schipperke 23, there are lots of others that are rare breeds but have been around quite some time.
Many breeds have registrations under the 300 a year mark that aren't British breeds.