.4, Your first point is the crux of the matter. The estimate is something like 10 years before 'new' staff outnumber 'old', then a huge amount of pressure can (will) be brought to bear to close the present scheme. Promotion dependent on you signing up to new pension, higher pay rises for those on new scheme there are hundreds of 'incentives ' that management can use.
This has happened throughout our industry and throughout privatised companies.
Your second point, way back at the start of this thread foghorn said
Closing it is more to do with keeping a bunch of crystal-ball-gazing actuaries in the credit rating agencies happy than a sensible response to increasing longevity.
As NATS is so heavily geared (and the higher it's credit rating, the cheaper it's borrowing) the company can save so much more by having a AAA credit rating than the start up costs of a new scheme.
High credit ratings are achieved by reducing long term liabilites (like pensions).