meat pie,
As HD has previously said, why not go straight for ATCO with NATS?
But to add an answer your question. These days there is a shortage of ATCO's. More and more of the smaller airfields are returning to training ATCA's to ATCO's (through one of three colleges).
Why?... They have the advantage of maybe a couple of years to get to know the ATCA, and therefore a chance to assess there suitability to pass the training. Also a lack of ATCO's in general, and competition for the one's out there.
If you follow this route, you will either by bonded for around 3 years per rating, or required to sign a loan agreement of some kind. This just helps to guarantee your commitment to stay at the unit that has just invested 10's of thousands of £'s in your training.
Also as HD said, a good ATCA is worth their weight in gold. Yes you will get some mundane jobs, but you will also have alot of responsibility.
Each unit will utilise ATCA's in different ways. Try to visit some units to see what they do.
A packet of biscuits is usually all you need to secure a visit.
