THE former Scottish baron Malcolm Huntley Potier, who is in jail for twice plotting to murder his former de facto wife, has launched a fresh attempt to gain his freedom under the ancient law of habeas corpus.

Potier is serving a 13-year sentence for soliciting a hitman to murder Linda Oswald, the mother of his daughter, and her lover in 2000, and again plotting against Ms Oswald's life while in Long Bay jail in 2002.

The former multimillionaire property developer, who acquired the title of baron when he bought the Scottish island of Gigha, has maintained his innocence and intends to appeal his first conviction to the High Court of Australia.

Yesterday, Potier told the NSW Supreme Court that if a miscarriage of justice was proved in the first trial, the second trial would also miscarry, as his previous convictions were told to the jury as tendency and coincidence evidence.

Representing himself, Potier said he was seeking the issue of writ of habeas corpus, a legal action from 17th-century England through which a prisoner can be released from unlawful detention, after his most recent bail application was refused.