Indeed, Reginald Gill was convicted of fraud for making such claims. Gill is a particularly evil example of 'healers', persuading his victim, Stephen Hall, to stop taking his morphine. It is possible that with proper treatment he could have lived months, with Gill's IFAS machine and diet/supplements he only lived weeks. Of course it is entirely possible that Hall would not lived any longer with conventional treatment, but at least he would have had a chance.
John Vernon is another person caught using the IFAS machine to cure cancer. Unfourtunately I don't think he was prosecuted, though he was exposed by the BBC
As for Ms Knowland, she does indeed claim to have successfully treated cancer. However she also points out that she offers no guarantee. A fine line.