NHS -the early days

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I've just finished reading a novel set just after WW2. It focused on the role the new NHS had in beating TB. I was surprised to read that even in the early days , the government was surprised that "the middle classes signed up in their hundreds of thousands " as the original thoughts were it, and National Insurance, would only be taken up by the poorer lower classes.
This was all before my time.
Is this how it was?
When did it evolve to be free for all?
July 5 1948 – The NHS is born. When health secretary Aneurin Bevan launched the NHS at Park Hospital in Manchester (today known as Trafford General Hospital), it is the climax of a hugely ambitious plan to bring good healthcare to all. For the first time, hospitals, doctors, nurses, pharmacists, opticians and dentists are brought together under one umbrella organisation to provide services that are free for all at the point of delivery.
Source: https://www.nhs.uk/NHSEngland/thenhs/nh ... y1948.aspx

I was two and a half at the time !