If only social policy were as simple as a soundbite.

Runaway dads is the latest one from the Prime Minister, who calls for fathers who abandon their families to be stigmatised in the same way as drunk drivers.

It’s a point well made in political terms at a time of deep public spending cuts. Feckless fathers who abandon their families are a handy scapegoat for people juggling their budget to cover higher bills and upset at the closure of local services.

Stigma, however, is a slippery concept, particularly in the hands of politicians attempting to apply it to a social ill. Like a poultice, it will draw out underlying poisonous matter. And Mr Cameron’s condemnation is less likely to spur those fathers who fail their children financially and emotionally to fulfil their responsibilities than to unleash the censoriousness and prejudice that make life more difficult for all families headed by a lone parent.

If this Father’s Day sermon was a deliberate emulation by the Prime Minister of King Canute, we might just be getting somewhere. He commanded the tide to turn back in the knowledge it was futile to demonstrate he knew the limitation of his powers. Mr Cameron, however, appears to be shouting helplessly at the waves.

They are already lapping at his government’s plans for pension reform. It is a classic example of the knotty problem at the heart of welfare provision for governments of all political shades: whatever system is used to allocate benefits (and almost all of us are recipients at some point as children or pensioners ) is seen as unfair to some groups. Decades after equal pay and sex discrimination legislation, equalisation of the qualifying age for men and women is long overdue. That was already in hand by raising women’s pension age to 65 by 2020. Raising the qualifying age for both sexes to 66 is also necessary to take account of increasing life expectancy. However, by accelerating the change, around 500,000 women will lose over one year’s pension without sufficient warning to make alternative provision, some of whom have already taken early retirement through ill health or to care for family.

In this case, the rushed timescale is the result of the urgent need to reduce costs but it is yet more evidence of the need to base social policy on agreed principles. When it comes to welfare reform, however, we are doomed to return to Groundhog Day with every change of government.

Opposition politicians always have plenty of ammunition to criticise the benefits system as expensive and ineffective. In office, they bring in carefully-nurtured policy changes born of a genuine ambition to do better. Iain Duncan Smith is the latest example. His Universal Benefit is the result of the admirable intention of ensuring that people are better off in work than on benefits.

Most initiatives come unstuck, however, largely because calculations based on reducing cost and more accurate targeting of the most needy fail to take account of the exceptions. And life at the margins is full of exceptions. Even a modest financial cushion makes it easier to bounce back from blows such as redundancy, divorce or illness and those with skills find their way back into work more quickly than those without.

How to narrow that gap was the remit of that the independent review on poverty and life chances set up by the Coalition Government under the inspired chairmanship of Frank Field. As a Labour MP he was asked to think the unthinkable on welfare reform by Tony Blair but his most radical proposals are those that emerged from the poverty review at the end of last year. They recognise the importance of a child’s earliest years and suggest concentrating financial help and other resources on the youngest including supporting their home environment.

That was possibly what Mr Cameron had in mind in emphasising the importance of fathers but support for new families seems more likely to help them forge strong bonds than heaping shame on those whose relationships don’t stand the strain.