Is such a system sustainable though? Isn't England in a massive hole of debt? And if that debt comes due, what would happen to the quality of the NHS?

Almost Every western country is in a massive hole of debt, the us included.

I think it is more sustainable than other systems, especially the one practiced in the US.

Also, please note than in the US, public spending on health is already huge, and there’s a huge private spending as well - iirc about 20% of us GDP is spent on healthcare, which is double any other western country, and with worse results to boot. It is already unsustainable.

> Isn't England in a massive hole of debt?

The UK has a lower debt-to-GDP ratio than the US.

https://en.wikipedia.org/wiki/List_of_countries_by_public_de...

Their debt ratio is predicted to slightly lower by 2022, while ours is expected to continue to increase.

https://en.wikipedia.org/wiki/List_of_countries_by_future_gr...

Don't forget that the US spends by far the most per capita on health care world wide. The NHS saves money.