Brown advisor calls for tax breaks for stay-at-home mums after warning over nurseries

Professor Jay Belsky warned that toddlers who spend long hours in nurseries or with childminders suffer "disconcerting" effects.

These include difficult relationships with their mothers and aggressive and disobedient behaviour when they start school.

Those who spend time in centre-based care from a very young age are particularly at risk, he said.

Professor Belsky, the man brought in to assess the Government's Sure Start family centres scheme, made his plea for change "on humanitarian grounds".

He said that tax policies should reduce - rather than increase - the pressure on parents to leave their youngsters in the care of others.

The findings will come as a deep embarrassment to Labour, which has pumped £21billion into subsidising childcare and toddler education over the past decade.

It has been heavily criticised for pressing mothers back into the workforce by giving out large sums through the tax credit system for them to spend on nurseries.

Ministers have insisted that the only way for two-parent families to ensure they stay out of poverty is for both parents to work.

Around £10billion of the spending has gone into Mr Brown's favoured Sure Start scheme, where family centres, increasingly concentrate on providing childcare.

Professor Belsky and his team on the £20million evaluation project have published no major reports in two years - not since they showed that Sure Start was doing more harm than good for the worstoff children.

He has made no public comments in Britain during this time. These latest remarks were made to a seminar held in Germany in July.

Professor Belsky, the director of the Institute for the Study of Children, Families and Social Issues at Birkbeck College in London, said that both US and British research points in the same direction.

"The risks are that more hours in any kind of childcare across the first four-and-a-half years of life and, independently, the more time in childcare centres, the higher the levels of problem behaviour," he added.

There is also evidence "that children who spend more time in non-maternal care through their infancy, toddler and pre-school years experience somewhat less harmonious mother-child relationships through their first three years".

He said they "start school being somewhat more aggressive and disobedient than children with less non-maternal care experience".

These "disconcerting" effects can not be blamed on poor-quality childcare - and "seem more likely and longlasting when children experience centrebased care early in life".

Professor Belsky said that although family background has a bigger influence on development, "more and more children seem to be spending more and more time and younger and younger ages in nonmaternal care arrangements in the English-speaking world".

He added: "This means that small effects, when experienced by many children, may have broad- scale consequences."

He called for policies to help reduce time spent in childcare, in particular "centre-based care" - and to give a parent the opportunity to stay at home if they so wish.

"Tax policies should support families rearing infants and young children in ways that afford parents the freedom to make child-rearing arrangements that they deem best for their child," he added.

The system should "reduce the economic coercion that necessitates many, at least in the U.S.A and the UK, to leave the care of their children to others when they would rather not".

The professor said the effects are less in "high-quality childcare", which should be encouraged.

His definition of quality is thought to be based on well-trained staff and good child-staff ratios.

"All of these conclusions could be justified on humanitarian grounds alone," he said.

Mr Brown has attracted criticism both for Labour's insistence that all mothers should work and for giving benefits to working single mothers.

A final report on Sure Start was due to be published in 2006, but nothing appeared.

The most recent major piece of analysis came out in December 2005.

In it, Professor Belsky and his colleagues said that middle-class families had taken advantage of the Sure Start facilities and the poorest were shut out.

However, Mr Brown endorsed the network by pumping in an extra £4billion during the summer.

Professor Belsky's team is understood to have submitted a new report to be published over the next three months.

The American-born academic, 56, said of his comments in Germany: "Tax policy should enable parents to make choices. When they choose childcare, it should be good quality childcare."