The national health services in the countries of the British Isles are considered a World Health Service by foreigners. HIV treatment is vastly expensive and many other treatments too. It is often used as a human rights issue to prevent expulsion.
Over £180m was estimated to be owed to the NHS by foreign patients and the doctor's trade union the BMA both demands more money for their members whilst opposing charging foreigners for their treatment.
Telegraph: https://archive.ph/5B5YZ
£180m: https://archive.ph/Lq629
BMA: https://www.bma.org.uk/advice-and-support/ethics/refugees-overseas-visitors-and-vulnerable-migrants/bma-view-on-charging-overseas-visitor