NI is used to fund the NHS. "The fund" has money taken out of it. At various times where have been below the surface political arguments that not enough of the money was going to the NHS. A proportion is siphoned off to the NHS. The fund is just more or less in real time (it's more complicated than that and why it's led to arguments) it's not a pot of money that's been safely stored away from the past for many years. It was meant that the fund would be put on something of a more sustainable and robust system, but this never happened because the UK's penchant for spending lots of money on nuclear weapons in the 1950s, the korean war and in general the 1951-64 tory government which apart from housing didn't really do very much for 13 years and were a bunch of penny pinchers.
Politically it wasn't talked about that much in the 50s and 60s to voters because the public would think the politicians of the time were irresponsible morons. There are some famous examples of what labour politicians had to say about it from those days. As in other countries like the US in the late 60s and 70s focus was on how to make the things run and offer as wide a range of services as possible.
https://commonslibrary.parliament.uk/research-briefings/sn04517/
Politically it wasn't talked about that much in the 50s and 60s to voters because the public would think the politicians of the time were irresponsible morons. There are some famous examples of what labour politicians had to say about it from those days. As in other countries like the US in the late 60s and 70s focus was on how to make the things run and offer as wide a range of services as possible.
https://commonslibrary.parliament.uk/research-briefings/sn04517/
