And as I pointed out: If you think they are too strict, then you can pay for a private insurer to cover things the NHS doesn't cover or won't do fast enough for you.
Note that this is a very good cost containment strategy. Note also that this can probably not reduce patient outcomes at all. Note also that it is extremely unpopular.
https://www.cms.gov/medicare/medicare-fee-for-service-paymen...
The named defendant was the Secretary of Health and Human Services. The suit was over practices followed by Medicare contractors, but it's not like they were operating outside the knowledge of Medicare, they were acting as Medicare had directed them to act. The settlement agreement has Medicare changing the procedures the contractors will follow.
"...in which the plaintiffs alleged that Medicare contractors were inappropriately applying an “Improvement Standard” in making claims determinations for Medicare coverage involving skilled care..."
I'm hazy on the details myself, but briefly:
1. Healthcare insurers are covered under ERISA, the Employee Retirement Income Security Act, of 1974. Among the provisions of that act are limitations on the right to sue, under the theory that a retirement fiduciary is an agent of the employees. It's been a long time since I've looked at this, and I don't recall all the specifics, but yes, there are some limitations on suit for lack of coverage.
https://en.m.wikipedia.org/wiki/Employee_Retirement_Income_S...
2. Lawsuits against the government are possible and happen all the time. I'd have to see what specific limitations apply, if any, to Medicare, Medicaid, Disability, and VA care, but you'll find numerous instances of suits:
https://duckduckgo.com/?q=lawsuit+medicare+denial+of+(care%7...
Update, additional info on ERISA and its impact on lawsuits: appeals through the insurer must first be exhausted, but statute of limitations applies whilst lawsuits are blocked: https://www.lawyersandsettlements.com/articles/stock_option/...
With what money? And furthermore, what good will that do if you die before the trial is over?
There's an enormous information and power imbalance in the health insurance contractual relationship. The large number of medical bankruptcies by people that had health insurance is surely a testament to this fact.
Edit: Let me also add this; when you sign up for health insurance you're entering into a contract with the insurer. They have to be up front about what they're providing and it's your obligation to understand what you're buying. With the government you don't get that. You get whatever the vanilla flavour of healthcare coverage is today. There's no contractual obligation, only whatever the government says is right today. You don't get a guarantee. Because there's no contract you can point to, even if you're legally allowed to sue (and I don't think you are.) you won't have a case to stand on.