Just for clarification, the NHS budget in the UK for 2016/17 was £120 billion[0], which works out to be about £1800 per person. Seems like a pretty good deal, given that in the US, health insurance for an individual would be around double that [1].
There's also a large amount of coercion in keeping mentally ill people locked up in a prison because the government won't pay for them to receive treatment in the community, of course...
You're right that we can't say "no coercion happens in the NHS", but we can reasonably say "any coercion that happens in the NHS is orthogonal to its single-payer nature". CTOs are definitely in the grey area between the legal and healthcare systems.
[0] https://www.gov.uk/government/statistics/public-expenditure-...
[1] https://resources.ehealthinsurance.com/affordable-care-act/m...