Jen,
Don't forget that you also need a letter from his employer (BT??)

The letter needs to confirm:-
- the sponsor's current employment status and the length of employment.
- the type of employment (permanent, fixed-term contract or agency etc).
- gross annual salary
- the length of time the sponsor has been paid at the level of salary stated in the application.

I suggest he best approach the main HR department and or the Payroll department .

The letter should be on company headed paper and preferably signed-off by a manager

Just needs to be a statement from the company really.