Dee Mac
I don't have access to the current version of the Trust Deed so I can't give you section numbers but, and this is from notes I made when somebody gave me access to an earlier version of the Trust Deed, Part 1 defines non pensionable earnings as:
Non-Pensionable Earnings means the aggregate of (1) that part (if any) of a Member’s remuneration from the Employers which is declared by the Employers to the Trustees to be non-pensionable and (2) the value of any benefits in kind received by the Member from the Employers.
In subsequent parts of the Deed which define benefits non pensionable earnings are excluded so by declaring a part of the renumeration to be non pensionable NATS can make the change. They've previously done this for a whole variety of payments including apparently AAVAs. (My grade doesn't get those so I've never taken much interest in the agreement). You would need to check the latest version of the Deed to be sure but it is unlikely that section has changed. I had expected people to ask to see the Trust Deed at the meetings but it hasn't appeared on NATSNET yet.
Not Long Now's option C doesn't apply to the Trust Deed. Nobody can change it without an Act of Parliament or agreement of every member regardless of the state of NATS. But the Deed does cover in great detail what the Trustees have to do in those circumstances and closing down the scheme is an option.
Option C does apply to the Trust of Promise which contains clauses limiting it's effect if NATS is in financial trouble. That document was recently published on NATSNET if you wish to read it.