Re: "Opt Out"?
"Only if you're processing exclusively under consent as your justification. The NHS, from a GDPR perspective, is very unlikely to ever use consent as its justification."
Hmm...
"Mainly because it doesn't need to,"
What's your reasoning here? Not legally required, not necessarily in legitimate interests, the vast majority is not vital interests, not public task (because this isn't a public task) and not necessary to fulfil contract.
Consent is all that's left. Same as everyone else.
"The NHS would still need to gain consent for anything it's doing with your identifiable data, but that's grounded in medical ethics and the Caldicott guidelines, rather than GDPR."
Sadly the NHS abandoned medical ethics long ago. Doctors routinely hand over patient data to all and sundry, including Google, without consent.