NATS is, without a doubt the best option. If you can get a cadetship all the course costs are paid for you and you also get a salary, not much, but with other allowances it's survivable. The downside is that you won't get much choice as to if you want to do aerodrome or area control.
If you can't get a cadetship for whatever reason then your options are limited to either Cwmbran or ASTAC, in both cases you have to pay up front for the full costs of each course and if you fail at any stage, you'll be kicked out with no reimbursement of course costs whatsoever.
As far as employment is concerned, not withstanding a cadetship, you have two options:
1) Get a job at a non NATS airport as an ATSA, do your time, usually 18 months to two years, then apply for any internal ATCO training schemes which may be available.
Pros: You don't have to pay for any costs, you get your salary and all expenses paid while you are training, if you don't make it, it's highly likely that you'll be able to walk back into your ATSA job.
Cons: You might have to sign a bonding agreement, although less common these days.
2) Pay for the initial aerodrome course yourself and approach an a non Nats airport to get them to pay for the APP and APS course if you are successful.
This is not as uncommon as some folk may think and is a good ploy if you are absolutely confident of passing the first hurdle.
Pros: You get a salary and costs paid during the APP and APS costs, guaranteed job if you pass.
Cons: Fail any part of any of the courses and you are out on your ear.
Best of luck to you.