If you don't get into NATS, try the Eurocontrol training scheme.
If that doesn't work, try and get a job as an Air Traffic Control Assistant at a regional non NATS airport.
Despite the recession, most regional airports still have training schemes to train their own atcos but you'll have to put in a couple of years or so to get the experience and knowledge required.
Think very, very carefully before self funding (around £40k+ depending on what you want to do course wise).
ASTAC or Cwmbran are both very good at what they do and will offer you a pre course assessment to see if you stand a chance of getting through the course, but you should be aware that if you fail to make the grade at any stage, you'll be invited to leave with no ATCO licence, no refund and no job.
Getting the courses via an existing employer is by far the better option and if you should bomb out at any time, there's a reasonable chance that you will be recoursed at a later date.
There is always the military option, but if you join up you are an officer first and atco second and as things stand, you cannot convert your military licence into a CAA one when you leave.