Pierre Lellouche, the French Minister for Europe, is a fluent English speaker and a man unafraid to express his views. He is entitled to voice his disagreement with David Cameron’s stance on Europe. It may be useful to hear his warning that the Conservative leader’s promise to repatriate powers from Brussels is unrealistic. It is less helpful to hear his crude depiction of Britain having “castrated” its influence. What is absolutely unacceptable, however, is his description of Conservative policy as “bizarre autism”.

Autism is a serious, lifelong and disabling condition, affecting more than half a million people in Britain. To use the term “autism” and “autistic” in a derogatory or flippant manner can cause deep hurt to those affected by the condition. To use the term as a criticism, for dramatic effect or to try to gain political advantage, perpetuates the misunderstanding of this condition and is, as the National Autistic Society said yesterday, “extremely unhelpful”.

Enough popular prejudice already surrounds this distressing condition, often wrongly labelled a disease. Huge damage has been done in recent years by the absurd and spurious claim that the MMR injection can cause autism. Not only did this lead to many children being unnecessarily exposed to the diseases from which they are protected by the jab, it also detracted public attention from the search for ways to help those with autism to integrate into society.

In recent years the incidence of autism has appeared to rise, largely because of a sharp increase in the diagnosis of the condition. In fact, while there may now be more cases in absolute numbers, for reasons yet to be identified, better medical analysis and diagnoses have now recognised as autistic children who in the past were simply labelled mentally retarded. The means that autistic people can be better treated — and their condition seen not in the unhelpful category of retardation but as a specific developmental disorder.

Research suggests a strong genetic link to autism. But this has also proved controversial. There are three traits that, taken together, constitute a definition of the condition: a problem with communication, difficulty in social interaction and a pattern of repetitive behaviour. All these traits are present, to a greater or lesser degree, in most people. Is autism, therefore, merely an extreme end of a normal condition? Certainly, the seriousness of the condition shows wide variance. Some people, with Asperger syndrome or mild autism, are less affected; in others, autism is so pronounced that normal education and independent life are impossible.

Genetic research may soon help to unlock the causes of autism, much as it is revealing the causes of so many other debilitating conditions. Treatment and understanding are also improving fast. Special schools have been built across the country for the severely affected. With a necessarily high staff-pupil ratio they are costly to run. But remarkable results can be achieved in the best. Two years ago The Times made one, TreeHouse, the subject of our Christmas appeal, and a generous reader response has consolidated the work of this pioneering institution. Disability is, increasingly, understood as something that need not remain a barrier to a rewarding life. But it is no subject for poor jokes or political insults. That is something Mr Lellouche should learn — fast.