RogerOut, you do have to give and take a little (OPM etc) however in reality I think you will find that NATS are saving a good deal more than 6% with the pensions holiday - if my memory serves me well the "employer" contribution to the NATS (ex CAA) pension scheme was in the region of 12%!!!!!!!!! - all of which makes your point even more strongly!
It's also true however that NATS will also have to pay increased employer NI contributions, so as pointed out this is hardly a point that will gain much sympathy from NATS. Also whether we "care" that NATS is part private or not does not alter the fact that it is - and the government will certainly not re-nationalise (except for war).