Under TUPE conditions pension doesn't need to be matched like other T's & C's, therefore fairly easy to see how to construct a rival bid that is less, when you have a smaller pension provision overhead to factor in.
There is a caveat though; Any NATS employees that has been in employment since before part privatisation has a security blanket to protect the pension they currently receive if NATS loose any contracts, i.e. Birmingham, Gatwick. If the incumbent provider doesn't match the pension, NATS have to offer them a job elsewhere within the business. A large number of employees have exercised this right at Birmingham, maybe more than expected, and who knows how many at Gatwick also have that option and then choose to do the same.
This may open up opportunities to ATCO's from other units, as happened at Birmingham, but the training backlog created by this can be huge and in many ways only a success with the contribution and not an immeasurable amount of goodwill of the current ATCO's that are OJTI rated within the unit.
It could be argued though that in a few years any contracts lost by NATS, or indeed any new ones that they want to look at in the UK could be bid for with lower overheads as they would no longer have the burden of the final salary pension to factor in. They would be a leaner meaner company with a more competitive edge.