Ian Huntley last night began a life sentence for the murders of Holly Wells and Jessica Chapman - as his history of preying on children was revealed.

Home Secretary David Blunkett announced an independent inquiry into how Huntley was able to get a job as a school caretaker despite accusations of rape, indecent assault on an 11-year-old and a string of relationships with schoolgirls.

The parents of the murdered ten-year-olds described their daughters' killer as "a time bomb just ready to go off" as the revelations about his history emerged.

And they told how he imposed "a life sentence" on them when he lured the two best friends into his home on Sunday, August 4, last year and killed them.

Jessica's father, Leslie Chapman, said: "Our life sentence started last August. His is only just beginning."

Mr Chapman, 52, made no attempt to conceal his hatred as he said: "I hope that the next time I will have to see him will be like we saw our daughters, and it will be in a coffin."

Huntley, 29, showed no emotion as he received two life sentences for the double child murder.

His accomplice and ex-fiancee Maxine Carr was sentenced to three and a half years for conspiring with Huntley to pervert the course of justice, but was cleared of two charges of assisting an offender.

She will serve half that sentence, including the 16 months she has spent at Holloway awaiting trial, and will be freed early next year.

It is understood she will be held in Durham Prison.

Trial judge Mr Justice Moses told Huntley he had shown "persistent cruelty" and "merciless cynicism" towards the girls and their families.

He said: "Your tears have never been for them, only for yourself. In your lies and manipulation up to this very day you have increased the suffering you have caused the two families."

Addressing Carr, 26, he said: "You had plenty of opportunity to refuse to persist in a course of lying and deception. You chose not to. If you had the slightest true regard for those girls or families you would have told the truth."

The Old Bailey jury of seven women and five men deliberated for 17 hours and 32 minutes, and returned majority guilty verdicts of 11-1.

They rejected Huntley's claim that the best friends died accidentally at his home, 5 College Close, in Soham, Cambridgeshire.

Huntley, the former caretaker at Soham Village College, claimed the girls, wearing their Manchester United shirts, went into the house because Holly had a nosebleed.

He tried to convince the jury during more than two days of testimony in the 30-day trial that Holly drowned in the bath and that he killed Jessica as he tried to silence her screams.

But Huntley - who had claimed the girls left his house alive and changed his story just days before the trial was due to start - admitted he had dumped the girls' bodies in a remote ditch, cutting off their clothes and burning their corpses in a bid to cover his tracks.

The jurors knew Huntley had once been charged with raping a teenager, a charge that was later dropped.

What they did not know was that he was also accused of indecently assaulting an 11-year-old and having sex with a string of other schoolgirls.

The authorities involved have admitted that the system of checks failed, allowing a man who had come to the attention of Humberside Police on ten occasions to get the job.

In fact, police searching for Holly and Jessica only found out about the rape charge when members of the public rang them.

Huntley's tissue of lies in the witness box means that only he knows why he killed the girls.

The prosecution claimed he had a sexual motive - a belief supported by his sordid past and the fact he laundered his bedclothes after the deaths.

But his efforts to erase all evidence of his crimes, aided by his besotted fiancee Carr, meant detectives were unable to prove just what happened when the two girls fell into his clutches.

Carr, who worked with Huntley's victims as a teaching assistant at their primary school, lied to protect her lover of three years.

Some of the relatives of Huntley's victims sobbed quietly in the courtroom as the verdicts were returned.

Holly's father Kevin, 40, said he felt "a great sense of relief" as the verdicts were announced, adding: "There was certainly no sense of euphoria."

He went on: "We have had doubts for 16 months. Not until that verdict was announced today have we had a cessation of our fears."

Mr Wells said the families wanted to be involved in the inquiry announced by Mr Blunkett, and said he hoped changes to the law would mean that no other families suffered in the same way.

The Chief Constable of Humberside David Westwood, whose force investigated allegations of rape and underage sex against Huntley between 1995 and 1999, said there were "system failings and elements of human error".

The Home Secretary said there were real concerns about the way police handled intelligence on Huntley's past. "This has been a shocking and horrific case and my thoughts are with Holly and Jessica's families," said Mr Blunkett.

"I cannot begin to imagine the pain they must have endured during this dark time.

"I hope they will find some comfort in seeing the man responsible for this wicked act brought to justice."