Why don't you buy yr UK pension entitlement via the NI Voluntary scheme (it's just gone up but still a a bargain) & go private in Spain for health care.

It's a lot cheaper than Autonomo for pretty much the same benefit if you are self employed & you have the choice.

See a good accountant in Spain, a small fee is easily over recovered.

Absolutely! If you actually earn money (or sweeties) from "duties performed" in a the UK you are liable for tax on it in the UK irrespective of whether you are a UK resident or not.The same rule will apply in Spain.

If you are working in Spain, you either need to be working for an employer or on your own account as self employed. In both cases tax is due from day one of starting work. If self employed you would also have to register and pay the social security payments.

Most of the discussions about tax and tax residency on this forum relate to people who are not working and usually receiving UK pensions or some other form of unearned income. This is an entirely different situation as the income is not being generated from "duties performed" in Spain.

With unearned income from outside Spain residency is key, as if you are tax resident, you pay on your worldwide income - if non resident you only pay tax on your Spanish income.