Medical

All up in the air with brexit. If your planning something in the future, wait to see what happens post 1st April.

Our retirement is a few years off yet, but hopefully there will be some agreement as medical bills are not nice.I lived in the US for 7,years so I have experienced this

Regarding health cover, to become a legal resident, both EU and non-EU citizens have to either be able to transfer their health cover from their country of origin to the Spanish health system, or to have private health insurance prepaid for one year and covering all eventualities including pre-existing conditions. 

There is recent legislation about free health for all, but this conflicts with the residency legislation. Unless the residency legislation is amended, then what I said above will continue to apply.

At the moment, if you are over UK retirement age, the Overseas Healthcare Team at DWP UK issue you with a letter confirming your eligibility which you then take along to your local INSS office in Spain. They give you a document which you then take to your nearest Centro de Salud and you get a SIP card which entitles you to exactly the same as a Spanish resident. At every stage you will be asked for various documents, with copies, and few people will speak English so an interpreter may be needed.
As Jim says, all this may change but if you refer to the DWP pages they will be updated as and when firm agreements are in place. Spanish healthcare is very good but learning Spanish in the meantime will help you immeasurably.
If you do decide to move here in the future, make sure you get your medical records from your UK doctor before you move.
All the best because all things being equal, it´s a beautiful life here.

Can I also ask if you are not of retirement age can you buy into Spanish Healthcare System (not private health insurance) and how can you apply for this.  Any advice would be appreciated.

I found this for you although I´m not sure if this would suffice for becoming a resident here so you may have to pay up front for the first year´s private medical insurance. Hopefully someone can be more precise on this.

Purchasing public health insurance – Convenio Especial. If you are not covered for state-run healthcare through any other means, the Spanish regional health authorities offer a special pay-in scheme (convenio especial). ... However, prescriptions are not subsidised at this rate so you would pay 100% of prescription costs.Spain: healthcare - GOV.UK
https://www.gov.uk/guidance/healthcare-in-spain

Gilly, you have to be resident for twelve months before you can buy into the state system:

https://www.costablancaforum.com/area/almorad%C3%AD-spain-11/healthcare-medical-advice-in-almorad%C3%AD-16/jims-guide-convenio-especial-buy-into-state-health-care-36444/

But watch this space, as some communities like Andalucia seem to be applying the free for all scenario.