That's an excellent question, and a great demonstration of why the legal mechanisms surrounding a government-run medical system can make it so dangerous. A government that legally prohibits anyone from paying the cost of medical care for themselves or their family members has no moral right to exist.
Any government system must place such restrictions on the market. Remember, that was a key component of HillaryCare...
It is all about centralized control leading to equality of outcome. As a result, we must not ALLOW people to be free of any government restriction!
I don’t know for certain, but I would be confident in placing a bet that the restrictions are in place in the UK system.....