There is an interesting article in the Telegraph here
NHS rejects expats returning from Spain - Telegraph about changes to reciprocal healthcare for Expats in Spain. Best to read the whole article but key points are:
"Tough new regulations mean that many can no longer access local health care services there, but those returning to the UK are also being turned away by the NHS, despite the fact many have paid National Insurance throughout their working lives."
Previously, ex-pats taking early retirement were entitled to free health-care in Spain:
"Until now these expats have been able to get medical treatment in Spain, under a reciprocal agreement, where costs were refunded by the UK Treasury, provided that patients signed a “residual S1” form (previously known as an E106). This form confirmed that expats had paid National Insurance for the past three years in the UK, and the British Government would therefore cover necessary medical costs overseas.
But these forms are being withdrawn on July 1. Protection will remain in place for those who have signed the forms before this date, but only until their form expires – and they last a maximum of 30 months."
"From July 1 2014 you will no longer be able to apply for a residual S1 (formerly residual E106) under which you could currently be entitled to up to 30 months of UK-funded healthcare if you retire early to another EEA country."
Also expats cannot receive non-emergency treatment back in the UK without being resident back in the UK for 6 months.
More info can be found here
https://www.gov.uk/healthcare-in-spain &
Early retirees rule change - healthcare abroad - NHS Choices
Rules for those who HAVE reached retirement age are different. "If you are a UK state pensioner this will not affect you – S1 forms will still be issued to state pensioners."