TAD,I've been at LHR for nine years. For the first four years of that there was no real assessment selection process. In that five years we had over ten ATCOs come to us from other units...most from 'busy' units such as TC and AC. Only one validated. Since we've introduced a selection procedure the validation rate has increased dramatically.I think the reasons for such a procedure are sound, and to be honest I'd expect that if I wanted to move to another unit. Why shouldn't I?