The government appears to be backing down on two disastrous policy ideas: compulsory participation in the Green Deal and the tax cap on charitable donations. Having argued strongly against both measures (here and here), I'm delighted to learn that the former will be scrapped and the second put out for consultation. Both proposals very clearly ran counter to the Conservative belief that families, businesses and institutions should be encouraged to solve problems for themselves rather than relying on the state to tell them what to do.

I hope that David Cameron's intervention in these recent blunders is a sign that he recognises the need to clarify the Conservative message and get a grip on policy developments before they hit the headlines. In particular, as Paul Goodman pointed out yesterday, he should pay close attention to policies emanating from his coalition partners, since it was the Liberal Democrats who advocated both the “conservatory tax” and the charity tax.

With this in mind, perhaps it would be a good idea for Number 10 to scrutinise the interview Nick Clegg gave at the weekend, in which the Deputy Prime Minister promised to recruit 65,000 “nannies” to improve social mobility. This new army of childcare workers will be expected to provide 15 hours of care a week for the 260,000 two year olds currently being raised in households with an income of £16,000 a year or less. The cost to taxpayers will be £650million. Mr Clegg declares that he is “obsessed” by this idea, which was first announced in last year's Autumn Statement and has since been claimed by Liberal Democrats as one of their key achievements in government.

Mr Clegg is not troubled by the likely cost in these times of austerity; indeed he says he's proud to be “shovelling in resources” at unprecedented levels. The cash will be given to local authorities to recruit the necessary childcare staff and set up or extend nurseries, where toddlers will be supervised on an adult:child ration of 1:4.

The Deputy Prime Minister believes the money will be well spent because it will improve social mobility: getting poor two year olds ready for school so that they will be less likely to be overtaken by their more affluent classmates later. It's also being touted as a way to get mothers of young children back to work, another issue on which Mr Clegg feels strongly. In this latest interview Mr Clegg reiterates his view that households where mothers who stay at home while their menfolk go out to work are a relic of the 1950s.

The trouble is that most families in Britain do not share his outlook. Whilst their children are very young, the majority of mothers want to be able to spend more time at home, not less. Their chief motive for returning to work is financial necessity. And for the poorest families in Britain, the offer of 15 hours of free childcare a week is in any case unlikely to enable them to take up work. Once they have deducted the time involved in getting their children to nursery and fetching them home again, there might just be time to get a load of washing on or prepare a meal; certainly not to hold down a job.

The care young children receive during those 15 hours will have to be of a very high standard if it is to entice parents to use it. For taxpayers who will be funding it, there must be good evidence that it will guarantee better outcomes for children than if they had stayed at home. For the toddlers experiencing it, there will also have to be very clear evidence that time spent in institutional rather than family care is happy and positive, rather than stressful and harmful.

These are high benchmarks which cannot be met simply by glib assertions about social mobility. Yet there is simply no evidence that these criteria can be met. Earlier this year the National Audit office reported that the free nursery education for 3 and 4 year olds has done nothing to improve their educational abilities at the age of 7 – a report which might have been expected to halt the expansion of the scheme to younger children. Studies by child psychologist and childcare experts both in Britain and the US have concluded that institutional care for the under-3s does more harm than good, having adverse effects on behaviour and driving up young children's stress levels. Babies and toddlers who thrive best are those receiving home-based care from a parent or grandparent, where they do not have to compete for attention or deal with a succession of different childcare staff.

Mr Clegg apparently believes that bright children from poor homes are being held back by bad parenting and should spend less time with their families. What an insult to parents earning less than £16,000 a year! Leaving aside the extraordinary assumptions built into this worldview, it is also baffling that Mr Clegg believes state-sponsored childcare workers would do a better job. As a study funded by the last Labour government concluded, the most important influence on child development is not income, or even schooling, but parental commitment and the extent to which parents engage in activities with their children. Putting even younger children into state-registered care for part of the day is at best irrelevant and at worst, harmful.

In contrast to the Green Deal blunder or the penalty on charities, this new and patronising nanny state proposal has so far received scant press attention. Maybe that's because its cost and implications have yet to sink in. However, as with other policies labelled “Made by Liberal Democrats”, it deserves closer scrutiny before any more money is wasted.