I've paid privately several times for my first wife for consultations (which is the soviet equivalent of a brown envelope, for the Stalinist NHS
and is a useful method of NHS queue jumping where you miss one or more stages of 3-6 month queues
and is sometimes with the same consultant you see in his private capacity.
) and for operations for several reasons, not available on NHS (perfectly valid reason), waiting list is unacceptably too long or in one instance, cheapest operation we didn't want and NHS insisted they wouldn't do what we wanted, so when we told them we were getting it done privately, the surgeon didn't like it and said he would do what we wanted if possible, but cheaper version if not, so we went private and the preffered operation was not possible, so had to settle for the easier one, but we know the doctor did his best to perform what was the better but not possible solution, whereas where I didn't trust the NHS I'm not sure I would have been so believing of the NHS one.
I've also found private consultations good value for money £50-200, considering the amount of waiting time you are bypassing.
At the end of the day you are in effect paying twice, but you have to be pragmatic and play any system to get the best outcome possible, even if not the best value for money.
One of the big problems with the NHS is the multiple 3-6 month waiting times for each consultation before you get near to any treatment. If they don't have any budget left each consultation these days will be just inside the NHS waiting limit so the hospital don't get bad rating marks and is often with one with different skills but available, so you are no nearer to getting treatment.
This of course has a prfound effect on a persons life if they are incapacitated and/or can't work.
When I'm Health minister in TB's government this will all be fixed of course as part private payment will be not just allowed, but positively encouraged as it will increase the amount spent overall on health. Personally, I can't see any problem in patients paying for the treatment or medicines not available on the NHS and NHS paying for the parts they cover.