Feeding babies on pureed food is unnatural and unnecessary, according to one of Unicef's leading child care experts, who says they should be fed exclusively with breast milk and formula milk for the first six months, then weaned immediately on to solids.

Gill Rapley, deputy director of Unicef's Baby Friendly Initiative and a health visitor for 25 years, said spoon-feeding pureed food to children can cause health problems later in life

She blames the multimillion-pound baby food industry for persuading parents that they need to give their babies pureed food. 'Sound scientific research and government advice now agree there is no longer any window of a baby's development in which they need something more than milk and less than solids,' Rapley said.

The industry in Britain is worth more than £450m, compared with £191m in 1989. More than four out of five of Britain's one million babies aged between four and 20 months eat and drink baby food worth more than £120m a year.

Until recently, the words 'baby food' conjured up nothing more exciting than a bit of stewed apple and a rusk. Now, supermarket shelves groan with jars of organic, fresh ingredients, with some ranges even seeking to tempt the discerning baby with 'superfood' options and local ingredients.

Makers of baby food say they are taking Rapley's study seriously. 'This is very new research and we need to look at it very carefully,' said Roger Clarke, director-general of the Infant and Dietetic Foods Associations, a group representing such manufacturers as Heinz, Nestle, Boots and Nutricia.

'UK infant food companies support a flexible approach to feeding infants, but the age at which solids are introduced depends on the nutritional and developmental needs of individual infants and a "one size fits all" policy is not appropriate,' he added. 'Generations of mums and dads have relied on the simple convenience of these special recipes as part of their baby's diet to provide safe, sound nutrition with a wide variety of tastes and textures - from purees that are easy to suck straight from a spoon to soft lumps that encourage chewing.'

But Rapley, who has produced a DVD explaining how to follow a new feeding programme called Baby-Led Weaning, points to an increasing number of scientific projects and government guidance that she says support her programme. 'In 2002, the World Health Organisation backed research that found breast or formula milk provided all the nutrition a baby needs up to the age of six months,' she said. 'That research said feeding a baby any other food during their first six months would dilute the nutritional value of the milk and might even be harmful to the baby's health.'

After six months, Rapley says, babies are capable of taking food to their mouths and chewing, making purees and spoon feeding unnecessary. 'The World Health Organisation was so impressed by the research that it rewrote its recommendations on baby feeding,' she said. 'A year later, the Department of Health for England and Wales followed suit.'

Offering babies pureed foods once they can chew is not only unnecessary, it could delay the development of chewing skills, Rapley believes. In addition, allowing a baby to take as much or as little food as it needs stops it becoming constipated.

Rapley believes that babies allowed to feed themselves tend to become less picky, develop better hand control more quickly and to avoid foods to which they are later found to be intolerant. Rapley was inspired to investigate the widely accepted use of pureed foods during her quarter-century as a health visitor. 'I found so many parents were coming to me with the same problems - "my child is constipated, my child is really picky" - and they couldn't get them on to second-stage baby food. So I started to wonder what would happen if we never took the control away from them in the first place,' she said.

After years spent observing babies and conducting her own studies, Rapley developed her feeding programme, which teaches that babies over six months should be in charge of what goes into their mouths and when. 'Provided a child is sitting up straight and is supervised by an adult, he or she can feed themselves a variety of healthy finger foods with their hands,' she said.