Sometimes you read a story and whoop with joy. Ha, ha! Ho, ho! Sheer glee! One thing's for sure, when they hear this in St Mellons the laughter will ring out louder than anywhere. John Redwood, the Vulcan, has taken up with a thrice-married former model!

It is a reminder that of all the world's splendours, sex is a never-ending source of wonder and delight. Reports talk of Nikki Page's taste for transparent dresses and dominatrix thigh boots - probably tabloid exaggeration since she's also a former Westminster councillor and former London mayoral hopeful. But in a spirit of generosity Redwood has so often lacked, it is a moment to rejoice in the infinite and bountiful joys of human love. When Major Andrew, his constituency chairman, says "he's almost a new man - and a lot more fun", that's reason to celebrate.

This normally sober and responsible column does not usually approve of prurient tabloid outings of anyone's private life, and strongly supports a privacy law. The sexual doings of politicians may be interesting, but their revelation serves no public interest. It only deters good people from entering public life at all.

But no privacy law would apply to any public figure discovered doing something utterly at odds with their public pronouncements. So, for example, those telly evangelists caught in serial sexual misdemeanours while earning mega-money preaching old-time morality would be exceptions. Politicians and vicars would be covered by the law - unless they had made it their very specific stock-in-trade to preach against sexual sinners.

And unless it was a politician like John Redwood who, as a once obscure secretary of state for Wales, made his name by leading his party's charge into the valley of family values, marriage and vengeance against single parents.

He launched his assault 10 years ago with a visit to St Mellons, a poor estate in Cardiff, vilifying the lone parents there. So the fact that he has split from his (now vengeful) wife, thus creating a single-parent family (albeit not a teenage one), would certainly be a fact for public consideration. For he never acknowledged that single motherhood descends on women of all ages and conditions - married or not - for many reasons, as indeed do unplanned babies (ask the prime minister). Redwood's campaign of blame against single mothers was opportunistic and cruel: now the public can see it was also hypocritical.

They were nasty days. John Redwood's notorious visit to St Mellons branded it forever as a den of female vice. St Mellons was a place, Redwood said, where there was "no presumption in favour of creating a loving family background". Subsequently he said that "the assumption is that the illegitimate child is a passport to a council flat". The single mother is "married to the state". If the father cannot be found, grandparents should be made to pay or adoption be considered. The welfare state was offering "incentives to entice young women to become mothers before their time". "Single mothers are costing 4p on the standard rate of income tax."

When the attack reached a crescendo at the Tory party conference, as Peter Lilley sang his poisonous Gilbert and Sullivan spoof about "single mothers who get pregnant just to jump the housing queue", even the usually supine George Carey, then Archbishop of Canterbury, stepped in to protest at this monstering of the vulnerable. Redwood replied crisply that preaching marriage was only "good Christian doctrine".

This eventually led to the cut in lone parent benefits that was the legacy Lilley bequeathed to Gordon Brown, passed in the dying Tory days as a deliberate landmine for Labour to implement. Since Labour pledged to obey every jot and tittle of Tory tax-and-spend plans, Brown gritted his teeth and insisted this first test of his iron chancellorship must pass. How Lilley gloated. A short time afterwards the money - and a great deal more - was restored, but symbolic damage was done.

Why this Tory assault on single parents? The worst scar of their 18 years was soaring poverty and here was an easy scapegoat. In the early days they said that as the rich made more, it would trickle down to the poor - but by the 1990s it was undeniable that while the rich had got richer with massive 38% tax cuts, the poor were much poorer. So the blame was shifted from the deliberate government policy that had made the income gap worse on to the collapse of traditional family values.

It went with the grain of old Conservatism and it was at least partly true. Because unequal pay means most women cannot earn enough to be sole breadwinners, because there is no childcare, one-parent families are usually condemned to poverty. (Last week's Policy Studies Institute research showed for the first time conclusively that children of single parents do worse because they are poor, but only as badly as children of equally poor married couples.)

But the Tories' empty blame and moralising came with virtually no policy prescription. True, it led to the child support agency getting a bit more money out of fathers, a good idea. Otherwise moral blame was just an excuse to cut benefits. It was all pure cynicism: they didn't believe this moralising stuff. Consider the hypocrisy of what John Major and Edwina Currie were up to, even as he demonised the most helpless women and children.

There is little which democratic governments can do to change the social and sexual mores of the times: great liberal reforms - divorce, gay rights - only catch up with changed behaviour. A draconian withdrawal of all benefits and housing might have forced people to marry or have babies adopted, but mercifully no government that tried it would last long. Hardly a family is without close relatives who are divorced, single mothers or living together unmarried. At least Labour knows the answers to teenage pregnancy, even if they are not yet implemented everywhere: sex education; easy access to contraception and the morning-after pill via school nurses; intensive education support if they do have babies; and raising girls' horizons. Teenage motherhood is a symptom of poverty - and now numbers are falling.

Opinion polls show no one - and surely not even John Redwood, now - wants to go back to locking people for eternity in miserable marriages. Love blooms and he too seems to have been liberated by a Labour era in which these things are understood with more kindness than he ever offered to single mothers.

All this is worth recounting for younger readers, or those with fading memories, as a reminder of just how nasty the Tory era was. There is nothing about the current Tories to suggest that, when it next suits them, they would not again find bullying the poor for their moral derelictions a useful excuse for cutting benefits and programmes. Lest we forget.

· p.toynbee@theguardian.com