An NHS consultant will have a defined NHS contract stipulating hours/terms and conditions. Outside his/her contracted hours working for the NHS, they can work privately.
The consultant may have a be part-time NHS contract (and be paid pro-rata).
Some GP's are technically self employed (but only have 1 client, the NHS), they pay 26% of income into pension ATM, but many GP's are employed (employed by GP partnerships or directly by the health board), and a few work as private GP's - mostly in London.
There are strict rules about what private work GP's are allowed to do (they can't just charge NHS patients for services that they should provide for "free"). So insurance medicals for employment reasons for example - people pay for those, as the NHS won't.
40+ hours? My DH has been working as a GP for 20 years, I don't think he has ever had a week where he's worked anything like 40hrs, typically the "half-time" partners at his practice work around 35hrs a week and the full time ones 60+hrs - DH has taken on several additional roles in the area of health service reforms ...... for which, he has pointed out, he gets paid less than the cleaner..... this takes him up to 80 or so hrs a week. He works most days with no lunch break or other breaks. He is choosing to do extra work (the health service reform roles) of around 20hrs a week because it is benefiting (actually saving lives), in the exceptionally deprived area he works in.
He is getting pretty hacked off with the constant Daily Fail style "GP's are over-paid and must be punished" comments. Having a high income does not mean you are overpaid. I think the NHS gets excellent value for money from my DH and his partners - they are worth every penny and more. They work in an a very challenging environment dealing with some of the most socially and economically vulnerable families in the country.