I quite agree about the 'health tourist' angle. In theory my husband could have needed a very expensive operation/treatment once arrived in UK, having contributed nothing all his life. There must be a way to avoid this, but I can't think of one. One can hardly refuse to treat a seriously ill person and leave them to suffer/die. Maybe candidates' sponsors should provide a large sum of money in a Trust Fund which can be accessed by the NHS to pay for expensive treatments. Another option might be a very thorough medical examination to ascertain that the applicant is in reasonable health before they arrive. My husband had only to prove he didn't have TB, but this only applies to certain countries, and is primarily intended to prevent infection of UK inhabitants. Then of course, the new arrival could suddenly become ill/have an accident and need urgent medical care, in spite of having passed the medical.
I wonder how other countries cope with this? As they don't have an NHS, presumably that puts everyone on a level playing field, and new immigrants would be paying the same as the native population for private medical care?