New figures have revealed that almost 1,500 additional patients with suspected autism in Buckinghamshire, Oxfordshire and Berkshire are waiting for a diagnosis this year.

It comes as waiting lists have expanded across England, with an autism charity warning the "diagnosis wait crisis" is taking a toll on patients' mental health.

They have called on the Government to "urgently fix this broken system".

Figures from NHS England show there were 204,876 patients with an open referral for suspected autism across the country in September, a 27 per cent rise from 161,827 the year before.

In the NHS Buckinghamshire, Oxfordshire and Berkshire West Integrated Care Board area, 8,825 patients were waiting for an autism assessment, up from 7,380 last year.

Of these, 89 per cent (7,880) had a referral that had been open at least 13 weeks.

The NHS target is for every patient with a referral to receive a first appointment within 13 weeks.

Tim Nicholls, assistant director of policy, research and strategy at the National Autistic Society, said the figures should be "a huge wake-up call to the Government to urgently fix this broken system which lets down autistic people and their families".

"An autism assessment can be the first step to really understanding people’s needs and too often people can’t get support without a diagnosis, even though this shouldn’t be the case," he added.

"Waiting for months or years for an assessment leaves people struggling without the right support, increasingly stressed and anxious. It pushes some people to a mental health crisis."

He added without public investment the crisis would persist, "leaving autistic people, families and NHS services under the strain".

Just one per cent of the patients with an open referral for more than 13 weeks entering September in Buckinghamshire, Oxfordshire and Berkshire received a first appointment that month.

The median waiting time for a first appointment across England is 43 weeks.

"While there remains a high demand for autism assessments, we are seeing an improvement in the number of assessments completed.

"But we know there is more to do, which is why we have published new national guidance to help local partners deliver high-quality autism assessment services and to manage the 161 per cent increase in referrals over the last four years, while providing enhanced autism training for psychiatrists."