AFAIK know it's still closed, even though oddly enough the atcocareers website mentions nothing off this...
Quotes off facebook
NATS Careers - Air Traffic Controllers Recruitment needs for 2012 and subsequent years will be reviewed in the autumn and an update will be issued at that time.
We would like to encourage you to pursue your interest in Air Traffic Control, so please continue to view our website
www.atcocareers.co.uk for future updates.
We hope to receive an application from you for this rewarding career with NATS when our recruitment system re-opens. Good luck!17 August at 14:11 ·
So according to this it's still closed and new dates won't be released until late autumn, so I'm guessing in a month or so perhaps?