As Mo Mowlam has found out - colourful episodes from your past often have the unnerving habit of returning to haunt you just when you are hoping to set a good example for others.

Political commentators are predicting the "revelation" that Ms Mowlam inhaled cannabis smoke in her youth will not dent her position as leading the government's anti-drugs campaign.

However, in the rather more tricky world of household politics, tales of past wrongdoing can leave parents with some explaining to do to their offspring.

Oasis star Noel Gallagher - not so long ago a fierce advocate for drug taking - appears to be distancing himself from the seamier side of rock 'n' roll as fatherhood looms.

For the likes of Gallagher and Sir Paul McCartney - stars whose racy pasts were lived in the media spotlight - it is not a matter of if their children will find out, but when and who from.

Ordinary parents are faced with a greater dilemma - how much, if any, of their past should they share with their children.

Valerie Riches, director of Family and Youth Concern, advises candour with caution.

"There's no point in pretending you're an angel - no one has been. But you don't want emotional orgies of confession."

Given proper thought, sharing experiences of drug abuse, sexual experimentation or any of the other issues which mark our passage to adulthood can be instructive for both parent and child.

However, tales of past misdeeds can also fatally breach the parent-child relationship, leading to accusations of hypocrisy which undermine established family rules.

Susan Littlemore from Parent Line, stresses that tackling prickly teenage topics with admissions about your own youthful indiscretions is not a surefire winner.

"A quick comment from a parent can be a destructive thing."

She points out that many parents decide to confess to wrongdoings at highly-charged, stressful moments.

"If they find their child with a joint in their bedroom, a parent may just blurt out: 'It didn't do me any good. Why are you doing drugs?'"

Parents should also consider their motives for coming clean about their past conduct.

"Doing it to just off-load guilt is quite inappropriate," says Ms Littlemore.

The only reason to deliver, potentially shattering, home truths, is to help highlight serious issues. It should certainly not be done without thought or as part of a one-sided "sermon".

"It has to be based on good communications. Whatever a parent has to say - they have to think about how they are going to communicate that to their child in a constructive way."

As Mo Mowlam will doubtless attest - coming clean has its risks, but when seeking to tackle a problem, experience is often the best teacher