Continuing a point @D0c.Col raised in another thread:
The EASA regs don’t, and probably never will, recognise any UK class marks.
A UK-only class marked drone will be a legacy drone in Europe 
Unless the drone has for example both a C1 and a UK1 label on it. But can we see drone manufacturers around the world doing that? Especially given the way DJI hard-lock drones in to an existing EU class number with no way of ever changing it, who knows 