The UK uses Small as a wake category. Although some others may do likewise (Switzerland) it is unusual.
The UK spacings are
H-H,M,S,L
M-M/S, L
S- S,L
H-4,5,6,8NM
M-3,4,6
S-3,4
To all UK ATCOs, I believe these spacings are different from ICAO and the rest of Europe.
As for cleared to land when one aircraft is still to vacate... well, it does include a certain distance that not many regional aerodromes in the UK could accommodate. I'm out of touch but I think it says the preceeding aircraft must be 2500m further along the runway and in continuous motion? However, remember that this is used elsewhere in Europe... as is the 2.5NM on final approach within the last 10 miles.