The Cocker is split into varieties as opposed to breeds. They can still be interbred, as can the 2 varieties of Collie (Rough & Smooth), the varieties of Dachshund and the varieties of Beagle (13 & 15 inch). I have to check on the BTs, but I think they are separate breeds.
The Norfolk & Norwich terriers used to be all lumped into the Norwich breed, but were separated by ear carriage not that long ago.
And Corgis.
LOL