Basically you will be at the college in Whiteley for at least 7 months if you do a Tower only course, 10 months if you do a Tower and/or approach Course and at at least 11 months if you do an Area rating.
Once you've finished your training you will be sent where the company needs you. For tower only it will be one of the London airports, Tower and Approach can be any of the airports around the country where Nats provide the ATC, Approach only will be Terminal Control at Swanwick and an area rating will mean you'll either be working at Swanwick or Prestwick in Scotland.
You get very little choice about where you're sent, you can state a preference, but as the first you sign is something saying you're a mobile grade worker you don't have a lot of choice if the company wants to send you to Aberdeen and you want to go Bristol etc etc