Migrants' healthcare bills need to be recovered by hospitals, the Government has said after an expert warned paying for visitors is "absolutely unsustainable".
According to reports some people have arrived in Britain to go straight into treatment at a cost of thousands of pounds a day, while others have left the country before bills have been paid.
A spokeswoman for the Department of Health said officials are "determined" to ensure the system is not abused.
She added: "We were the first to introduce tough measures to clamp down on migrants accessing care and we are now focused on extending charging to other areas of healthcare, expecting to recover up to £500 million a year by 2018 from visitors using the NHS."
Cancer specialist Professor Angus Dalgleigh told The Sun that, with the latest medication for some diseases costing 100 times more than at the start of his career, bills had rocketed.
"The cost is huge. No other healthcare system in the world could cope with it and the abuse of this system must be stopped," he said.