The latest from the rumour mill is that ATSA numbers are not likely to be reduced significantly until 2015 due to NATS technological advances going into reverse...AGAIN!
So it's still worthwhile applying, you will probably start as an ACPO - Aircraft Position Operator (ATSA 1) in the simulator on a varied contract. The tower assistants are ATSA 2's but you will still be on a varied contract. ATSA 3's are permanant staff and work as sector assistants in the Area Control Centre. However, the Manchester Area Control Centre (MACC) is scheduled to move to Prestwick, Ayrshire in Jan 2010. So as you can see it's all a bit of a juggling act especially if you don't want to leave the NW!
Good Luck
