Doesn't this issue go back several years when NATS lost the ATC contract at Gatwick?
The new Gatwick company did such a 'great' job that they eventually handed it back for NATS to run. NATS inherited all the problems and a lot of them don't get resolved overnight, particularly with staff shortages.
Not that NATS are squeaky clean. Their recruitment and training policies over the last few years leave a lot to be desired.