As a Pensioner non resident but spending a great deal of time here. Can I register with a doctor/

 JulianX.

You misunderstood my meaning.

When I said it's for the individual to decide with the accountants help I meant how well you submit , present and illustrate your claim for tax residency to obtain your desired result.

It's not  an automatic concequence of taking Spanish residency.

It's 90consecutive  days for residency & 183 cumulative days for fiscal residency. Leave the country after 89 days & the clock starts again. You can be fiscally resident without being a resident &  vice -versa.

There is no requirement to pay tax anywhere unless you have an income. If you spend capital only there is no requirement.

If there is conflict between two , or more, countries about where you are tax liable then itcomes down to where is your family base.

 Ok Julian perhaps this may end the debate. The letter of the law is thus:-

If you spent more than 3 months in Spain in any fiscal year you need to register as resident. That process then makes you LIABLE for income tax unless and until you can satisfy the Hacidenda you are legally fiscally resident in the UK or any other state.

If you can then satisfy the HMRC of your UK fiscal status it's possible as a pensioner to be registered fully in Spain for healthcare as the original poster asked and not pay any tax in Spain.