@maddog37,
I'm sure there's a several number of foreigners working at NATS. I'm Polish and I've already applied and got through the 1st stage, therefore I don't think NATS does look at foreigners in any different way then on British people.
But definitely you need to have English on a very good level. I'm not saying mine is brilliant, but I didn't find any difficulties with it yet.
Just don't worry and go for it
