The World Health Organisation is reported to have launched an investigation into a possible link between vaccines that contain mercury and a rise in the incidence of autism among children in Britain.

The Public Health Laboratory Service will analyse records of 500 GP practices to check for a link between the use of vaccines and a range of neuro-developmental disorders including autism, says a report in this week's Sunday Times.

The number of children with mild to severe neurological problems, such as dyslexia and autism has risen sharply in the past ten years. The controversial MMR vaccine which some fear is linked to autism was introduced 1988.

But it is not one of the vaccines given to children which contain mercury. Vaccines containing mercury include the triple DTP injection against diphtheria, tetanus and whooping cough and some Hib vaccines for meningitis.

It is thought that an accumulation of mercury could damage the brain, central nervous system and gastro-intestinal tract and lower the child's immune system so it cannot cope with the MMR vaccine, which may trigger autism.

Research by the Scottish-based Action Against Autism group shows that the number of children in English schools who have received statements for special educational needs rose from 140,000 in 1990 to more than 250,000 in 2000.

In Scotland the number of children with a similar "record of needs" rose from just over 8,000 to more than 15,000.

There has been a similar steep rise in autism in the US where research has found a "statistically significant" link between mercury in vaccines and developmental disorders, including Attention Deficit and Hyperactivity Disorder (ADHD) and speech and language delays.

New figures showed this week revealed a 2 per cent fall in the number of two-year-olds in Scotland who have had the MMR jab

The Scottish Centre for Infection and Environmental Health has also shown that uptake of other childhood jabs has fallen by about 1 per cent.

Meanwhile a conference this week was told how acupuncture is being used to improve symptoms in children with autism.

Professor Virginia Wong and her team from the University of Hong Kong have used a technique called tongue acupuncture which they say works by stimulating specific points on the tongue thought to correspond to brain functions, the World Congress of Neurology London heard.

Autism is a complex development disorder which varies in severity and causes social interaction and communication difficulties. It is four times more common in boys than girls.