Are you in the UK on a visa where you paid the IHS fee?
The NHS covers a lot of healthcare needs, like prescriptions for a set fee (which can even be prepaid), hospitals, GPs etc. For private healthcare there are a lot of options, but outside employer sponsored plans, you may find them prohibitively expensive for what they cover. BUPA and AXA are common, there are others if you search though. None cover pre existing conditions that I have found so they aren't worth it to me.