Useful article, Bob. With reference to the original question, the article linked by Bob contains the following statement:
Former UK residents who return there to settle will be eligible for free NHS care immediately, according to the spokesman.
That was also my understanding. The key words are "who return there to settle" so it is important that you make it clear that you have moved back to the UK to live. They are not entitled to free health care when visiting, except for UK state pensioners, see below.
Another statement made in the article, which is important regarding the discussion between Peebee and me, is:
UK state pensioners who live elsewhere in the EEA will now have the same rights to NHS care as people who live in England. This applies to all pensioners who receive a UK state retirement pension and are registered for health care in Europe with an S1 form.
What it does not make clear is the mechanism used to achieve this. Since the article refers to April 2015 it is possible that the mechanism has changed since I had discussions with DWP back in 2013/2014. Equally, I don't understand the use of the word "now". UK state pensioners, who are registered in a health care system elsewhere in the EU, could always get treatment in the UK when visiting using an EHIC card.