Donald James Joseph Cameron has led a long and rich professional career, practising as a doctor, pastor and lawyer.

Or more accurately, he has pretended to. In reality, he is a conman who has spent 24 years in prison. In the latest chapter of his Walter Mitty-style life, Cameron _alias Patrick Thompson _ last week posed as a Queen's Counsel to file a case before Queensland's Court of Appeal.

As Dr Thompson he prescribed medication and even helped in a cancer operation in 1979.

He assumed the identity of the real Dr Patrick Thompson and opened a surgery in Cronulla, in Sydney's south, and was sprung when a colleague who graduated with the real Dr Thompson recognised Cameron was an imposter.

Police told the court Cameron actually believed he was a doctor.

"The defendant appears to be obsessed with the medical field and believes he is competent to practise as a doctor," police told the court.

As Pastor Don Cameron, he founded the Church of Love and Peace while serving seven years for false pretences in Borallon Correctional Centre.

But it is Don Cameron self-styled lawyer, barrister and now Queen's Counsel, that has authorities bemused and amused.

With more than 20 convictions since 1961 including stealing, false pretences, forgery and indecent assault, Cameron has never been admitted as a lawyer although he studied law in jail from 1980-83.

His latest legal vehicle, Toowong-based Remedial Justice Association Inc, was formed in September and has as patron One Nation state leader Bill Feldman.

Last week, Cameron launched a Court of Appeal challenge for clients Patrick and Paula Farnan to regain management of their Runcorn childcare centre from liquidators.

But at the last moment Cameron abandoned his clients who were forced to put their case unaided to three imposing judges.

"I had every intention of going in but I heard a whisper from a source at the counter not to,'' Cameron said. Mr Farnan said the couple's ordeal ended abruptly when he told the judges Don Cameron had prepared his oral submission.

"They started sniggering," he said.

Cameron came to fame in 1992 when he acted for rebel farmers George and Stephanie Muirhead, giving them legal advice to secede from Australia.

The fact a prisoner at a half-way house could perform such acts embarrassed red-faced prison officials who swiftly returned him to secure custody after watching Cameron on TV ushering the Muirheads past the national media at court.

More than 20 convictions has not stopped Cameron taking action in the Court of Appeal to be a barrister. Instead, the court declared him a vexatious litigant in 1996 after he launched 13 actions against Westpac.