"If it bring NATS to its knees, so be it."
Are you kidding me? Is that really an argument? What about the sustainment of the employer who provides pretty much (and still will) the best Ts and Cs you will ever find? Any administrator charged with sorting out a bust company is going to target the thing that caused it to fail - in the NATS case the pension scheme that was too expensive that the company went bust.
Hold at SATAN - purely a question and not trying to be provocative - does a no vote to show dissatisfaction work, or does it play into managements hands? They could turn around at that and say "well we tried, the offers withdrawn, we'll go ahead with what we want to do anyway" and we are worse off. That is just IMHO a more likely scenario as them coming back and saying "you know what, you were right, we'll remove the cap idea, keep the pension running for new members and look again at one of the many things we have already discounted cos they were worse ideas".