A UK-born paedophile deported to Britain from Australia will receive the highest level of supervision, the Home Office has said.
Robert Excell, under a sheet, was accompanied by police at Heathrow
Robert Excell, 67, was imprisoned for almost 40 years in Australia for a series of offences but was freed from jail in Perth because of ill health.
He landed at Heathrow on 30 July and was required to sign the sex offenders' register before being freed.
Children's campaigners have expressed fears he might re-offend in Britain.
A director of the Victims of Crime Trust, police officer Norman Brennan, said Excell was still "every parent's worst nightmare", and called for him to be locked up.
But a Home Office spokesman insisted: "Protecting children is the highest priority of the government and we do everything we can to ensure the public is protected from offenders where a risk can be foreseen".
Excell will be monitored under the Multi-Agency Public Protection Arrangements (MAPPA) by a team including police, probation officers, medics and social workers.
He could also be subject to a Sexual Offences Prevention Order (Sopo), which applies to offenders convicted of sexual or violent offences overseas and who pose a risk of serious sexual harm in the UK.
A Sopo can bar individuals from being alone with children or from being within a certain distance of a playground and breaching the order carries a maximum of five years' imprisonment.
Excell has spent 37 of the past 39 years in Australia's prison system for child sex offences dating back to 1965, when he raped a seven-year-old boy.
He emigrated to Australia aged 10 but never became a citizen.
The Western Australian state government once considered him so dangerous it vowed never to release him.
He has been freed from prison on parole three times and committed another child sex crime on each occasion.
He raped a nine-year-old boy while on parole in 1973, and a 13-year-old boy when freed again in 1977.
In 1981, he was once again freed on parole but was later convicted of indecent behaviour with a boy under 14.
The Australian authorities say they now consider him a "low to moderate" risk.
His deportation had been planned for March but the move was delayed by a police investigation into claims he committed rape while in jail in Perth.
But in June detectives said new charges would not be brought, clearing the way for him to be deported.
Last month, Western Australia Attorney-General Jim McGinty vowed Excell would never be allowed to live in the state on his release from prison and would be returned immediately to the UK.
Robert Excell has been in jail for almost 40 years
Norman Brennan described releasing Excell as "like releasing a time bomb into the community, never knowing when it is going to go off."
He said Excell was a "predatory paedophile", saying: "One has to ask why is a man who is still deemed to be so dangerous that the Australian authorities don't want him to walk their streets now at liberty to walk ours with limited monitoring?"
A spokeswoman for the Kidscape charity said: "It is a concern for us that he could re-offend - he has already demonstrated a huge pattern of re-offending.
"We see it as a 'loose cannon' situation and would be happier if there was some form of monitoring of him, but as far as we know he will just be placed on the sex offenders register."