@haltonapp - yes, of course they are. RAF ATC training, examination, validation, standardisation and supervision are all tightly controlled, documented and assured. As has been said already, HF happens. That is not to make light of the incident, but no system is fool-proof, especially with a human in the loop.
@Door_Slider - ATC training and RW training have nothing to do with each other at Shawbury. ATC training is all simulated.
@chevvron - Live tower training (using dedicated Jet Provosts) ended in the early 90s (I went through JATCC in 93 and was on an all-sim course).
One of the reasons for moving Northolt Approach down to Swanwick was to have the Northolt controllers sat with the Heathrow team in order to remove some of the coordination issues associated with such a tight piece of airspace.