A lawyer who agreed to a contingency fee arrangement with a client over a medical negligence suit will face the top court for professional misconduct following a disciplinary probe.

Contingency fees - whereby a cut of any damages awarded in a suit are paid to the lawyer instead of a legal fee - are prohibited in Singapore.

But Mr Jeffrey Lau See Jin, who began practice in 1991, was found liable for arranging an oral contingency fee pact after a hearing in March by a disciplinary tribunal appointed by Chief Justice Sundaresh Menon.

The tribunal, comprising Senior Counsel Jimmy Yim and lawyer Carrie Seow, found the charge sufficiently serious to refer it to the Court of Three Judges.

The tribunal, in its report released on Aug 1, said: "Where a lawyer agrees to take a direct cut of the damages or the claim amount, he acquires a direct interest in the litigation and this mode of charging forms the very rationale of the rule against contingency fees. His fees cannot be a direct function of the damages awarded in the claim."

Ms Serene Ng, the complainant, had been suffering from suspected severe asthma and was unhappy with the conflicting advice and treatment given by two different groups of doctors consulted.

She met Mr Lau through a mutual friend, Mr Steven Lee, in 2014 who suggested that she offer a cut of the damages to Mr Lau, according to her. She took Mr Lee's advice but did not know then that contingency fees are prohibited in Singapore.

At an April 2014 meeting with Mr Lau, she offered a 15 per cent cut of the damages awarded if she won but he counter-offered 20 per cent and sought a greater share if he won more than $5 million in damages.

Mr Lau, defended by lawyer Chandra Mohan K. Nair, disputed her version and denied there was an agreement on fees at the April 4, 2014 meeting, explaining he had told her then his charges ranged between 20 and 25 per cent of the claim amount.

The tribunal found the complainant to be credible and her subsequent actions "entirely consistent". While she was " forthcoming, honest and direct in her answers", Mr Lau was "unreliable as a witness as various aspects of his evidence were troubling and internally inconsistent".

Lawyers S. Ramesh and Ivan Lim, in prosecuting for the Law Society, argued that Mr Lau did not take any notes at the meeting because he knew he was entering into an illegal pact and did not want a record.

"Having regard to all these matters, we completely disbelieve" Mr Lau's testimony on what he told the complainant, the tribunal said. He was ordered to pay costs. The apex court hearing will be fixed in due course.