It's all taxes, and it all goes to the same pot, there's no hypothecation, the NHS budget is not related to the money brought in from NI contributions, and National Insurance is included in the tax revenue along with VAT, Fuel Duty, CGT, Stamp Duty, Income Tax, etc

NI is about 19% of tax revenue, Income Tax 27%, VAT 18%, local taxes (council tax and business rates) about 10%.

It doesn't include other receipts, things like profits from state owned business.

Total government revenue (about 10% higher than total taxation) does not cover total government expenditure, hence a deficit, and some branches of economics considers revenue and expenditure separate in a system which controls its own currency.

Either way, the US spends more on government healthcare (per head of total population) then the UK, the decision not to have universal healthcare isn't a funding one

I stand to be corrected. But deficit should also be included (it's to be paid by future generations or being paid by currency debasement).