<<my friend also who works in London for NATS has given me the general feeling that NATS is not exactly the best company in the world of ATC management to work for-can others explain why?>>
I've never worked for an outfit yet that some people were not dissatisfied with. I spent 31 years with NATS, and its predecessors, and was wholly satisfied. I had more time off than those in any other job you can think of and retired at 58 with a good pension too.
Now I know that things have changed, just as they have with every business. Pension schemes are getting hammered, staff levels being reduced, etc, etc. Nevertheless, I still think you'd be pushed to find a better employer in the UK for ATC work. I never got involved with any "extraneous" work like committee meetings, union stuff, etc., and never had any desire to get into management. I went to work, talked to the jets and went home... but then my priority has always been to get home! It suited me fine.
Good luck, but I think you're nuts to want to leave Oz!!