Helth Cover

If a foreign person is over on holiday I know they would normally have insurance to cover any treatment they need, but how does it work here in the UK? Firstly, do NHS hospitals charge foreign people whilst on holiday like they do in the US, and secondly if an illegal immigrant came here, and needed medical care for, let’s say a heart condition, would they be able to get it for free in our UK hospitals? My husband and I are disagreeing over this and I’d like someone to put the record straight!!