Training ATCOs costs a lot, usually paid up front by the ANSPs.
AENA found it cheaper to pay very generous overtime rates rather than employ and train the correct amount of staff. So much so that Spanish ATCOs were earning large salaries ( but still not the figures bandied about in the media).
The Spanish government want to privitise AENA so they briefed media with exagerated rates of pay while simultaneously increasing the hours worked by about 40% and capped salaries. All this with no negotiation.
At least that's my understanding of it.
As far as UK salaries go HD is on the money in post #2