And most commonly, patients who unexpectedly need the services of a hi-tech ICU after their operation. It's too expensive. Of course private patients pay national insurance too, and are entitled to the use of NHS facilities. You see my point. This exempts it and others from the many regulations found in the NHS, such as the ratio of specially trained ICU staff that must be on every shift, or the regularity with which patients must have their vital signs recorded.
Most juniors worth their salt are too tired to moonlight in private hospitals.
But the idea that you get an automatically higher standard of medical or nursing care however, is false. The NHS has well-structured machinery to investigate complaints. There are time limits imposed on the process, and outsiders, including lay people, are involved in the more serious cases. There is no investigative system whatever in the private sector. The only redress for the bereaved or injured is to complain to the GMC, or go to law.