Sorry to point out the obvious but how is tax changes related to pay negotiations? It isn't the company's fault what the government have changed the laws and you cannot expect NATS to pay you more just so your net monthly pay doesn't go down.
Mantovani has a good point, does anyone have the stats for the negotiated grade pay increases for the last few years? I know the bonuses a few of the top brass took, but how about the rest of them, did they get rises when we all got diddly?