A bill proposed by David Blunkett, the home secretary, fails to distinguish between innocent teenage fumbling and adult paedophiles when it outlaws ìsexual touchingî of under-16s.

If the bill becomes law it could theoreticially see teenagers facing up to five years in jail and land their parents with 14-year jail terms if they knowingly allow their underage sons and daughters to cavort with friends.

Blunkett had hoped MPs would approve the new Sexual Offences Bill but now faces a rebellion over its poor drafting when it is discussed this week.

He insists he has no intention of outlawing teenage necking, but his officials accept that, technically at least, his bill could have that effect.

The offending text, clauses 10 to 14 of the draft bill, says that a teenager ìcommits an offence if he intentionally touches another person (and) the touching is sexualî.

Under the new law, the teenage sweethearts Natasha Morris, 12, and Ashley Lamprey, 15, who met on holiday in Greece during the summer before running away from home together last week, could both face imprisonment.

Parts of the bill are designed to address the widespread public disquiet that followed the murder of Sarah Payne, the eight-year-old abducted from a field in Sussex three years ago and murdered.

In response, Blunkett had the bill drafted so that it would impose much longer sentences on convicted paedophiles. The bill also brings under one act a host of disparate offences.

It also introduces the new offence of ìgroomingî, under which paedophiles who approach youngsters through the internet with a view to meeting and abusing them will face a maximum of five years in prison.

But critics say that no matter how well intentioned the bill, Blunkett has gone too far. In trying to protect children from the attentions of predatory adults, it will criminalise them for innocent behaviour of their own.

Barry Hugill, a spokesman for the civil rights group Liberty, said: ìIím sure that the overwhelming majority of people in the country will believe this is silly. Most of them know the difference between abuse and teenagers snogging.î

The bill has been roundly condemned by the Family Planning Association (FPA) because it fails to distinguish between abusive relationships and consensual sexual activity between under-16s.

Rachel Hodgkin, a senior adviser at the FPA, said: ìThere is a maximum of five years for snogging or sexually touching someone. You could get the trauma of your perfectly normal sexual life as an adolescent being investigated as a major criminal offence.

ìThe net has been tremendously widened so that it includes French kissing and touching through clothes.î

Hodgkin said parents who supervised teenage parties at which under-16s kissed could find themselves at the mercy of the law.

A Home Office spokesman defended the bill as currently drafted: ìAdults do not have a monopoly on sexual abuse, and it is extremely difficult to come up with a formulation in law that will protect children from abusive sexual activity by children of a similar age while allowing for consensual sexual activity to take place.

ìWe believe that the law has to be crystal clear about the age of sexual consent, and any sexual activity below that age is not lawful.î

The spokesman added that guidelines would be issued to the Crown Prosecution Service, instructing it not to prosecute under-16s engaged in genuinely consensual sexual activity.

Blunkett had hoped the bill would face little opposition, but MPs on the standing committee examining the proposals will be told this week that it criminalises the sort of legitimate ó if awkward ó encounters enjoyed by millions of teenagers as part of growing up.

The bill has already been delayed by resistance in the Lords, where a majority of peers objected to its failure to outlaw sex in public lavatories.