It suggests that 83% of stammerers have experienced bullying, with more than 70% of this group saying it occurred at least once a week.

In half of all such cases, parents and teachers were said to be unaware of what was going on.

And nearly a third of those who were bullied as children because of stammering reported that the bullying had had lasting effects, such as low self-esteem.

The report, published in the British Journal of Educational Psychology, also says that children who stammer find it difficult to make friends.

It was written by Dr Siobahn Hugh-Jones of Leeds University and Professor Peter Smith of Goldsmiths' College, London.