“Reputations are tarnished at all levels” with such scandals, said Josef Woodman, who spent more than five years researching medical tourism and is the author of Patients Beyond Borders, a guide to finding offshore medical treatment. “This underscores the need for improved oversight and regulations that would help to prevent abuses.”

The Brunei case and another complaint from the United Arab Emirates accusing a group of Singapore doctors, including Lim, of overbilling may hamper the state’s ambition to attract more foreign patients in Asia’s $5.5bn medical-tourism market. Heart-bypass surgery in Singapore costs about a sixth of that charged in the US.

Lim denied any wrongdoing and in emailed responses said the Bruneian patient had agreed to the charges.

“The patient was never held to ransom,” Lim said. “She was willing to pay the price we had agreed to.”

India, Malaysia, Thailand and South Korea are among countries competing with Singapore for a slice of the industry, said Pawel Suwinski, a health care analyst at Frost & Sullivan.

 “Singapore is losing ground to cheaper countries and is evolving into a hub for complex surgeries,” said Wei Siang Yu, who owns Fly Free For Health, a Singapore-based medical concierge service.

Brunei is ruled by Sultan Haji Hassanal Bolkiah, the second-richest royal in the world, according to Forbes. The country’s health ministry sought a discount through its counterpart in Singapore on Lim’s S$24.8m bill for treatment of Pangiran Anak Hajah Damit, the Sultan’s sister-in- law, claiming the “extravagant” charges could harm the reputation of Singapore’s medical profession.