My family origins are in both Devon and Cornwall. When I was young, it was customary to serve clotted cream cool but not at fridge temperature. In this state, clotted cream is somewhat runny and jam should be spread before cream. Nowadays, people tend to serve clotted cream straight from the fridge and it will have the consistency of butter => cream first, then jam.
As for the Cornish, there were no signs of clotted cream in Cornwall in the 1960s and 1970s, until they noticed that several places in Devon were making good money selling cream teas. Twenty years later, the Cornish were claiming they invented cream teas.