The father of Babes in the Wood murder suspect Russell Bishop has intervened in the row over his mental state to claim his son is perfectly sane.

The families of Karen Hadaway and Nicola Fellows believe Bishop is attempting to be sectioned under the Mental Health Act to avoid being re-tried for their murders.

But Roy Bishop told The Argus his son, serving a life term for the attempted murder, sexual assault and kidnap of a seven-year-old girl, was "not mentally ill in any way".

He said: "We spoke to him just the other day and there is nothing wrong with him in that way at all. I would swear on my life."

Bishop was charged with strangling Karen, nine, and Nicola, ten, in Wild Park, Brighton, in 1986 but the case collapsed when forensic evidence was called into question.

He was jailed in 1990 for the attack on a seven-year-old in Devil's Dyke, Brighton, and is currently serving his sentence in Wakefield prison.

Sussex Police reopened the investigation into Karen and Nicola's murders last June and it is believed part of their inquiry involves new forensic tests. The double jeopardy law, which prevents someone from being tried for the same crime twice, is due to be scrapped for murder cases in April.

If deemed mentally ill, Bishop could be transferred to Broadmoor or Rampton hospitals and may not have to stand trial.

Nicola's uncle Ian Heffron, 49, a former policeman, said: "Somebody has orchestrated this. What better way of stopping an investigation than by saying, 'Sorry, he can't answer questions because he is mentally unstable'?

"Under the Police and Criminal Justice Evidence Act someone cannot be interviewed if they have a mental impairment. This is a tactic to help get Bishop out of a second trial."

Roy Bishop said: "I don't know where ideas Russell is mentally ill have come from but they are a load of old cobblers.

"It is perfectly untrue."

Mr Heffron, who lives in Wales, said the family would not rest until Nicola and Karen's killer was brought to justice. He said: "It has taken us 16 years to get rid of this archaic double jeopardy law.

"The first battle is won, now let's win the war. We want nothing less than a full and fair trial for him. I have no doubt Russell Bishop is guilty of the murders of Nicola and Karen and he must be named as such."

Mr Heffron said if the Crown Prosecution Service did not proceed with a new trial the family would pursue civil action against Bishop. They considered civil proceedings a year ago but were advised to wait as the scrapping of double jeopardy was imminent and Bishop could soon be tried again in a criminal court.

Mr Heffron said: "He must stay behind bars for the rest of his life. Society does not want the likes of him out on the streets. What right has he got to breathe the same air as you or I?

"If he ever does manage to get out we will be waiting for him. He will never ever walk away from what he has done."

A Home Office spokesman said they could not comment on a prisoner's mental health.