Don't worry!
This will soon all be a thing of the past as only last week the government announced plans to charge non-EU migrants 150% of the cost of any treatment they received. This article gives the details:
http://www.bbc.co.uk/news/uk-politics-28291276
For those of us not fortunate enough to have attended a private school it goes on to helpfully explain that "Under these plans non-EU patients receiving a £100 procedure could get a bill for up to £150"
It also explains "...for patients with a European Health Insurance Card (EHIC) trusts will be re-imbursed one-and-a-quarter times the cost of treatment, if they pass details on to the Department of Health, so it can then pursue payment from the appropriate European government." (Note: "If" not "When").
So far so good. Er...not quite.
Dr Mark Porter, chairman of council at the British Medical Association, warned: "Without more detail, there are question marks over whether or not these proposals will be workable and if the NHS has the infrastructure and resources necessary to administrate a cost-effective charging system. The NHS was not set up to recover funds at the point of delivery of its services"
Quite so, but neither was it set up as an International Health Service (the clue is in the name) and so it needs to adjust. There are plenty of idle hands on the non-medical side in NHS establishments. Some of them should be tasked with gathering credit card details instead of gathering data about patients' ethnicity and sexual orientation. Personally I believe there is not a cat in Hell's chance of the NHS collecting much in the way of cash from foreign visitors. The organisation is driven by ideology and any thought of protecting the taxpayer by collecting money from those not entitled to free treatment is dismissed as as heresy.