Sam Rodwell, 10, from Poole in Dorset, wore a T-shirt that said: "Autism - it's no mystery, it's mercury."

The slogan refers to the theory debated by some experts that autism is linked to mercury preservatives in vaccines.

The head teacher at Portfield School in Poole said Sam could not go on a school trip unless he changed the T-shirt.

PC gone mad

Janis Rogers, head of the independent school, told Sam's mother, Mandy, 45, her son could not go on the trip to a playground and park while wearing the shirt.

Sam's father, David, 45, said: "The staff felt that it was politically incorrect for Sammy to go out in that shirt and so they took it off and put another shirt on.

"He was very upset. It's political correctness gone mad. Who is to decide what is politically correct and what isn't?"

The school, which is run by The Wessex Autistic Society, has 64 pupils aged three to nine, and caters specifically for children with autistic spectrum disorders.

He does have mercury toxicity

David Rodwell

Bob Lowndes, chief executive of the society, said: "The Wessex Autistic Society fully respects the rights of parents to dress their children to their liking.

"However, the Society also has a responsibility to protect the dignity of the children in its charge at Portfield School.

"The shirt was changed as the child was due to engage in a public outing with other students and the shirt would have drawn attention to their disability which was not considered to be in their interest.

"We have a strong commitment to working in partnership with parents and are always happy to discuss such matters in an open and constructive manner."

But Sam's father said their policy was inconsistent because his son had already worn similar T-shirts to school.

He said: "It is a way of alerting people to his condition.

"Sam wears that T-shirt because he is mercury tested. We have had him tested and he does have mercury toxicity."