The payroll processing is outsourced to EDS, NATS staff handle queries, problems etc.
EDS lost the contract back in 2003 and since then it's been done in-house by the team in Edinburgh.
As a newcomer to the company, what you may find odd in NATS is that some things you'd ask payroll about in most companies... well, in NATS you need to ask HR. HR decide who should be paid what, update any grade/salary info etc. Payroll take those instructions and make sure it works, tax is paid corectly and that we all get our money on pay day. (they'll also tell you your tax reference
)
As for being disconnected from the rest of the company... It is a specialist financial service centre. If you call one of the payroll team you'll be talking to a payroll specialist who doesn't need to know all about ATC, they just need to know how to answer your daft tax code questions!
(they are also some of the lowest paid people in the company, so go easy on em!)