Lawyers acting for the man convicted of murdering Lin and Megan Russell in England in 1996 say they have new evidence of his innocence, including a "very detailed confession" to the killings from serial killer Levi Bellfield.

A British court has heard Michael Stone admitted to another prisoner bludgeoning Lin and Megan Russell to death with a hammer.

Appeal court judges have ruled Michael Stone must face a retrial over the murders of Lin and Megan Russell.