Plans to offer more drug treatments to child sex offenders to try to stop them committing further crimes have been announced by the Home Office.
The treatment involving libido-reducing drugs or anti-depressants would be taken on a voluntary basis.
Parents will also be able to ask for checks on whether new partners or people dealing with their children are known sex offenders.
It would be an offence to disclose the information to others.
Convicted paedophiles will also be subjected to lie detector tests if there is a suspicion they are targeting children.
Home Secretary John Reid said he was introducing 20 measures aimed at strengthening the way child sex offenders were dealt with.
He said the law was being updated to allow parents and guardians who had a relationship with someone who had unsupervised access to their children to register concerns about their child's safety with the police.
If that person was a convicted sex offender, the presumption would be that the parent or guardian should be informed, said Mr Reid.
SEX OFFENDERS CLAMPDOWN
Greater use of drugs to reduce sex drive
Parents' right to know background of new partners
Extension of satellite tracking
Pilot studies of compulsory lie-detector tests
Requiring offenders to provide passport, e-mail and internet details
£150,000 public awareness campaign
The scheme will be piloted in three areas, at a cost of £2m, as soon as legislation can be introduced - from around April 2008.
Mr Reid said allowing everyone to have access to information about sex offenders could drive paedophiles underground.
At the moment, employers can request a Criminal Records Bureau (CRB) check if a potential employee is going to work with children, while private citizens cannot.
Some of the most persistent sex offenders are already offered drug treatment, but the Home Office says this provision could be increased.
Mr Reid said more sex offenders would be offered drug treatment on a voluntary basis as part of a £1.2m package of improvements to treatment and supervision.
Offenders will have to provide more information including their e-mail, internet and passport details to the authorities as well as informing them if they begin a new relationship with a single parent.
And the Home Office will also introduce trials of compulsory lie-detector tests in the supervision of offenders.
David Davis, the shadow home secretary, questioned how the government would ensure that information passed to parents would remain private.
He also suggested that voluntary drug treatment was ineffective.
"The headlines today are about chemical castration. The reality is that while a voluntary scheme may be useful in some cases, it will not deal with the worst offenders who do not wish to conform," said Mr Davis.
He also complained that a national computer system, which was promised by the government in 2004 after the inquiry into the deaths of Holly Wells and Jessica Chapman, had been delayed until 2010 or 2011.
Nick Clegg, the Liberal Democrats home affairs spokesman, said he broadly welcomed the proposals as long as they could be made to work in practice.
Dr Donald Findlater, director of research and development at the child protection charity the Lucy Faithfull Foundation, said: "I think we have this notion that all sex offenders want to do bad things all the time. Some of them are desperately struggling with what's going on in their lives, and want help to be stopped.
"Some of them have been very enthusiastic about participating in lie-detector tests, and indeed would happily take pills if that will help."
Sara Payne, whose daughter Sarah was murdered by paedophile Roy Whiting seven years ago, welcomed plans to share information on sex offenders with parents but told the BBC that drug treatment should be compulsory.
"You're placing an honour based system on people that have already shown they have absolutely no honour.
The murder of Sarah Payne in 2000 prompted calls for new laws
"These are people that rape, molest our children, take photographs of what they're doing.
"They've already shown that they are the nastiest, I think the nastiest, people in the world because of what they do to children."
The US law, known as Megan's Law, named after Megan Kanka, seven, who was killed by a convicted sex offender, gives parents access to names and addresses of known paedophiles.
A campaign to launch a "Sarah's Law" - a UK version of the legislation - was launched after Sarah Payne's murder in 2000.
CHILD SEX OFFENCES 2005-6
Males under 13 sexually assaulted: 1,394
Females under 13 sexually assaulted: 4,645
Females under 16 raped: 3,152
Females under 13 raped: 1,389
Males under 16 raped: 292
Males under 13 raped: 363
Gross indecency with a child: 127
Source: Home Office
Children's charity NSPCC said it was pleased there would be no Sarah's Law because it could drive paedophiles underground.
But Steve Bevan, from Survivors Swindon, which helps men who have been sexually abused, said people had a right to know where sex offenders were living.
Harry Fletcher, assistant general secretary of probation union Napo, said Mr Reid's move to give parents information about sex offenders sounded "like a sop to certain tabloid papers".
"The information is not a commodity; it is highly sensitive and must be kept confidential," said Mr Fletcher.
A £150,000 publicity campaign has also been promised by the government to remind people that 90% of child sex abuse is carried out by someone known to the family.