Please refer to
this thread on an FoI request to NHS Direct. You will see that they say they receive no revenue from their 0845 number.
This (very long)
thread on Patientline discusses the problems with Patientline / NHS contracts, and what the NHS may indirectly get out of it.
This thread discusses the (ab)use of 08xx numbers for GP surgeries and has links to other theads on the subject.
Hope these are of some help.