<<I wonder how many of the people involved in initially selecting the 60-70% of failures are still employed by NATS ? Is there a chop rate for Instructors - i.e. if only x% of the course pass @ Hurn , are they dumped too ? >>
Why should they be? If you continue that argument you end up with simulator instructors and watche training officers being "dumped" too.
I spent 35+ years on and off training controllers and it is frequently impossible to determine if someone is going to validate until they start live training. I've seen trainees who have done well at the College and passed the exams with flying colours subsequently fail the live training. At one time the failure rate at Heathrow was about 80%. Such is ATC and it has little to do with the instructors.