Residency

You would be breaking the law. Having Residencia is not the same as Citizenship, you can have Spanish Residencia but still be a British Citizen. what you cannot do is be a Spanish resident and continue to use the NHS, if you are over state pension age you would register with the Spanish Healthcare System using your S1 obtained from DWP in Newcastle and if under State Pension age you would need suitable Private Health Insurance for at least the first year after which you could buy into the Spanish Healthcare System using what is called Convenio Especial. See the tab at the top of the Forum Homepage for Jim's Guides and reading them will provide much more information.

You can only be in one health service and one tax regime. If you want to keep your affairs in the UK, you will have to confine your visits here to less than 90 in any 180 days.

Your EHIC will only cover you for emergency treatment, and if you intend visiting Spain that much you should get private health insurance.

We are hoping to be able to stay at least 6/7 months of a year in Spain. We are both retired but not of UK retirement age. Still paying taxes and registered as self employed. 
What would be the best way forward for us.

Many thanks for your reply Ray.   I was under the impression that because our income is from rental properties in the uk our taxes would have to still be paid in the UK. 

from Spanish Solutions web page
Every­one knows someone who lives in Spain but still pays their taxes in the UK. There may be a reason for that. For ex­ample,UK rental income is taxed in the UK, but the per­son is still li­able for Span­ish taxes on this and may have to de­clare it, which is where the double tax­a­tion treaty comes into play.

The practice is that Spain require UK rental income to be declared, albeit any tax paid in the UK can be offset against tax due in Spain.

The problem is that, in the UK, expenses involved in letting out a property can be deducted from the income taxable, and the same applies in Spain until the end of the Brexit transition period, but after that expenses cannot be deducted.

Having to declare gross income rather than net will certainly result in tax being due in Spain as well as in the UK. Even though you are allowed to offset tax due in Spain by the tax due in the UK, there will still be tax due in Spain.

Once you get out of the UK system, which you can only do after your first tax return here, then I believe you should be able to stop submitting property rental returns in the UK, and just do them here.

Many thanks for the extra information. We will hopefully be able to get to Spain sometime this year to get all the above sorted in time.

Thanks again for your help and stay safe.