When the first signs of autism appear, GPs too often tell new parents that they are being over protective. Far too few GPs have real experience of spotting the early signs of autism and, if parental concerns are not taken seriously, a referral to a specialist with the necessary experience may never be made and intervention can be significantly delayed.

But the impact of a delayed diagnosis does not stop there. A clear diagnosis is the key to accessing all the other services a child may need. Without it, getting a statement for special schooling or the support of social services may be impossible.

Of course parents do not always spot the signs and if a GP or family nurse does not spot them either then a child might have started school before any problems are picked up. Many Autistic Spectrum Disorders are first noticed in school - not in a doctor's surgery.

And even when a diagnosis is made, it does not seamlessly begin a cascade of service providers fulfilling their obligations to the autistic child. Hence the shopping bags full of letters.

So how do we make things better?

First all GPs should be trained to spot the clues that could indicate autism. Second we need to ensure that a pathway is in place so that diagnosis triggers service supply.

The National Initiative for the Assessment and Screening of Autism has now published its National Autism Plan for Children (NAPC) which sets out a programme for identifying and diagnosing autistic spectrum disorders and providing access to early interventions for pre-school and primary school children. The plan recognises that there is no certain way to identify all cases of autism at an early age but proposes models and strategies by which assessment can be improved.

The NAPC, which was sponsored by the All Party Autism Group, the Royal College of Psychiatrists and the Royal College of Paediatrics and Child Health, has been acknowledged by the government which has also accepted that early diagnosis and intervention are important objectives. What we do not know yet is to what extent the NAPC will be funded and implemented.

The government has also promised an autism exemplar as part of its National Service Framework for Children. If that exemplar ultimately leads to a "one stop shop" where a diagnosis of autism automatically prompts the appointment of a key worker, able to access all the services the child needs, then it will deliver a step change in the quality of life for autistic people and their carers. But even if that is the case it will still depend on the initial diagnosis.

Looking beyond the need to improve diagnosis, and link service provision to it, there are areas of greater controversy. What causes autism? Is there a link with MMR or other environmental factors? Is the incidence of autism increasing or are increasing numbers an artefact of improving awareness? And when a diagnosis is made, what other medical interventions are appropriate? All these are areas of debate.

We need more research. The government commissioned a report from the Medical Research Council into the state of current knowledge and then awarded them £2.5 million to do extra work. It is a disappointment, however, to see that the MRC has as yet been unable to identify studies that meet its criteria. So far not a penny has been spent.

Most researchers in the field, and all the professional and learned bodies I am aware of, believe evidence linking autism with MMR is at best weak. Indeed there is better evidence linking autism to events in the early stages of pregnancy rather than post natal events. What evidence there is of a link with MMR does not, in my view, justify any change in immunisation policy that might threaten the development of herd immunity.

But in the absence of clear evidence of cause, and with the debate over incidence levels raging, parents are understandably concerned. Resolving these issues is the key to restoring confidence in MMR.

Parents also get angry when their own experience and observations of their child's welfare appear to be ignored. Many autistic children suffer severely from constipation and their parents often report that they thrive far better if it is treated aggressively. But many clinicians do not recognise the condition or prefer to treat it with mild laxatives rather than seek advice.

And - when a GP does decide a referral is called for - finding a sympathetic, autism-aware gut specialist is a problem. The team at the Royal Free became a "de facto" national centre of excellence for this type of condition but it was only funded to meet local needs and referrals from elsewhere in the UK have now been stopped.

Autistic disorders sit on a complex spectrum and the disorders that make up the full autistic spectrum may have different causes. They certainly present different challenges and require different support strategies.

We are, at least, making some progress addressing this complexity. But the day when MPs no longer have to read through shopping bags of letters from angry constituents remains some way off.