Most British pensioners abroad have spent their lives paying into the NHS through the years that they are least likely to use it and many continue to pay UK income tax after they retire abroad, seems quite fair for them to come back to the UK for some treatment.
In fact I think this is all an urban myth based on one or two cases.
Any one retiring anywhere in Europe where the medical system is so much better, there are many more hospital beds and specialists are so much more accessible would be mad to come back to the crumbling dirty NHS with such long waits to see specialists that many people pay to go privately.
For the last 30 years we have been domiciled in the uk where we spend 9-10 months a year and spend 2-3 months at our home in France. In that time we have made 300plus round trips by ferry to France, where we have often chatted to other passengers, in the winter, mainly second home or permanent French residents and we have yet to meet anyone who would come back to the UK for medical attention, when the system in their country of retirement is so much better.
I am not saying it doesn't happen, but the idea that every ferry and plane from Europe is packed with eldely retirees looking for secondrate medical treatment in the UK is ridiculous.