In the British Medical Journal, the team said breastfed babies may benefit from being given solid food earlier.
Current advice suggests weaning should occur at six months, but the UCL team say it could happen as early as four.
They suggest later weaning may increase food allergies and iron deficiency levels, but other experts backed the existing guidance.
Ten years ago, the World Health Organization published global advice advocating babies be exclusively breastfed for six months.
The research team, led by Dr Mary Fewtrell a paediatrician from the University of London Institute of Child Health, said it supported the recommendation for developing countries, where access to clean water and safe weaning foods is limited, and there is a high risk of infant death and illness.
But they added: "Many western countries, including 65% of European member states and the
But in 2003, a health minister said the
Parents 'cannot win'The WHO recommendation "rested largely" on a review of 16 studies, including seven from developing countries.
It concluded that babies just given breast milk for six months had fewer infections and experienced no growth problems.
There are a lot of babies being weaned before six months anyway”
End Quote Dr Mary Fewtrell ResearcherBut another review of 33 studies found "no compelling evidence" not to introduce solids at four to six months, the experts said.
Some research has also shown that six months of breastfeeding does not give babies all the nutrition they need.
Swedish research also found that the incidence of early onset coeliac disease increased after a recommendation to delay introduction of gluten until age six months, but fell back after the recommendation reverted to four months.
Dr Alan Lucas, director of the
"But in the
Dr Fewtrell added: "When you look at the figures, there are a lot of babies being weaned before six months anyway - and that's probably the most important thing in terms of hard evidence."
'Inappropriate feeding'But the Royal College of Paediatrics and Child Health and the National Childbirth Trust defended current advice.
And Janet Fyle, professional policy adviser at the Royal College of Midwives, said: "I really must challenge the suggestion that the
"I believe that this is a retrograde step and plays into the hands of the baby-food industry which has failed to support the six-month exclusive breastfeeding policy in the
"There is evidence that some babies do die in developed countries from inappropriate young child feeding, such as the introduction of solid foods earlier before their swallowing mechanism is mature enough or they have fully developed the capability to cope with solid foods."
And a Department of Health spokeswoman said: "Breast milk provides all the nutrients a baby needs up to six months of age and we recommend exclusive breastfeeding for this time.
"Mothers who wish to introduce solids before six months should always talk to health professionals first."
The Scientific Advisory Committee on Nutrition is to review infant feeding and is due to report later this year.