Britain's leading alternative medicine researcher has reignited a public row with Clarence House by branding the Prince of Wales a "snake oil salesman".

Professor Edzard Ernst criticised the heir to the throne for lending his support to homeopathic remedies and for promoting the Duchy Herbals detox tincture.

In a briefing with reporters at the Science Media Centre in London, Ernst warned that "snake oil salesmen are ubiquitous and dangerous", and named the prince as "one of the most outspoken proponents of homeopathy".

He later told the Guardian: "There are no official criteria for a snake oil salesman, but if they existed, I think Charles would fulfil them."

Ernst, who was Britain's first professor of complementary medicine, agreed recently to retire early from Exeter University, where he presided for 18 years over a unit that subjects alternative medicines to thorough scientific scrutiny.

Many of Ernst's studies have been damning for complementary medicines, with some proving no more effective than sugar pills. Other treatments, such as chiropractic spine manipulation, were potentially dangerous, he has said.

In a briefing that coincided with his stepping down, Ernst blamed earlier confrontations with Clarence House for the threatened closure of his department and his early exit as head of the unit.

The most serious clash came in 2005 when Ernst attacked a report commissioned by the prince into the economics of complementary medicine. Ernst was due to help prepare the report, but asked for his name to be removed after questioning its validity.

The report, led by Christopher Smallwood, a former economics adviser to Barclays Bank, claimed the UK could save billions by offering spinal manipulation such as chiropractic in place of mainstream treatments, and make further savings by prescribing homeopathy instead of standard drugs. Ernst described the report as "outrageous and deeply flawed" days before it was published.

The comments prompted a complaint from Sir Michael Peat, chairman of the Prince's now defunct Foundation for Integrated Health, to the vice-chancellor of Exeter University. The university responded with a 13-month investigation, which cleared Ernst of any wrongdoing, though he was later told that his unit would close in 2010.

While Ernst will still take early retirement, the department will remain open under plans drawn up by Professor Steve Thornton, who took over as Dean at Exeter in May. The university plans to advertise for a replacement for Ernst next week.

"The whole thing would backfire in my view tremendously if we found a promoter of alternative medicine and not a good scientist," Ernst said, adding: "It looked as though I had to go and that was the price for the unit to continue."

Clarence House said it would not respond to Ernst's latest comments, and added that the prince was unaware of Sir Michael's complaint in 2005.

A spokeswoman for Waitrose, which has exclusive rights to sell the Prince's Duchy products, said only that the Duchy Herbals range "complies to all the regulatory standards".