Levi Bellfield's confession to the murders of Lin and Megan Russell was "a sick joke", it was reported today.

Serial killer Bellfield last week claimed he was responsible for bludgeoning the mother and daughter to death in Chillenden in 1996. Michael Stone is serving life for the shocking crime.

Bellfield is said to have passed a statement of admission to Stone's lawyers, described as "an astonishing breakthrough."

It described how he'd worn "bright yellow Marigold gloves" during the attack, had pulled out on to the road in front of another driver and had thrown the hammer in the Thames before flying to Turkey.

He also admitted the unsolved 1990 murder of mum-of-three Judith Gold, 51, in Hampstead, and is said to have bragged about killing at least seven women, with 19-year-old student Elizabeth Chau, who vanished in West London in 1999.

Detectives are understood to be preparing to grill Bellfield about those crimes.

Bellfield said he'd take a polygraph test and last night The Sun reported two new witnesses have come forward since his confession: a "highly credible" one who saw Bellfield at the scene and a prison inmate who says the convicted murderer who testified against Stone was lying.

But today's Mirror quotes a source as saying the confession was now feared to be "a sick joke" to mess with Stone, who has always maintained his innocence.

The source said: “Bellfield is a narcissist who loves the limelight – he’s now saying he just wanted to mess with Stone’s legal team.

“He doesn’t appreciate the absolute heartbreak and anguish he heaps on the Russell family every time he publicly speaks about the crime.”

Bellfield, 53, is said to have now written to Kent Police formally distancing himself from the crime.

Stone had hoped the confession was a huge leap forward in his bid for freedom.

His sister Barbara Stone, 61, who lives in Gillingham, told KentOnline last week she believed the confession was "absolutely true."

Ms Stone, who has campaigned tirelessly for his freedom, said: "This is not just Bellfield chin-wagging.

"Nobody is going to come out with a statement like that over such a terrible crime.

"I have believed Bellfield for a long time but never thought he would have the guts to formalise a statement that can be used as evidence."

Bellfield, 53, is already serving life for the murders of Millie Dowler, 13, Amelie Delagrange, 22, and 19-year-old Marsha McDonnell.

He was also convicted of the attempted murder of Kate Sheedy, 18.

The confession document was due to be sent to the Criminal Cases Review Commission, which has the power to order re-trials and is considering an appeal by Stone.

The former drug addict has always denied responsibility for the killings.

He was convicted in 1998 and then again in 2001 after the original convictions were quashed.

Lin and Megan were bludgeoned to death at land off Cherry Garden Lane in Chillenden near Canterbury as they walked back from a swimming lesson.

A second daughter, Josie, was left for dead and the family's pet dog was also killed.