So there is more than one 'standard'?
The number indicates the date. The 92 tables are derived from data between 1991 and 1994 and were published in 1999. The 00 tables are based on data between 1999 and 2002 and were published in 2006. The 92 tables were the most recent available during the 2006 valuation. The 00 tables will probably be the most recent when the fund is valued again.
there would appear to be some flexibilty in which 'standard' to abide by. It does not seem unreasonable to suspect management have had an opportunity to make the pension fund look especially precarious in the run up to these negotiations.
Three things to consider. First the Pensions Regulator sets guidance which both trustees and actuaries have to follow. There is some flexibility but both trustees and the actuary would have to justify any use of that flexibility to the regulator. Second actuaries are "Professional" people and like all "Professions" have a code of ethics and a requirement to exercise independent judgement in their work. Failure to do so would lead to a very short career. Third although there are, as you'd expect, NATS appointed trustees they are not a majority and as trustees they have legal obligations to act in the best interests of the scheme at all times.