No doubt that the NATS scheme is excellent for anyone wanting to get into Airport Engineering, but if that doesn't work for you for whatever reason you could always try applying to a regional non NATS airport.
We have a training scheme for our own Tel's Engineers, training one about every three years or so - I know that doesn't sound much, but training is a long and very expensive process before we get the return of a fully qualfied engineer.
Clearly we, or most other airports, wouldn't pay as much as NATS, but you get all your training paid for and come out with the same qualifications as the NATS guys.
Once you've got a few years experience under your belt there's nothing to stop you moving on elsewhere (NATS Engineering included).