Around 172,040 people were on waiting lists as of December 2023 - up from 117,020 a year earlier and more than five times the 32,220 recorded in December 2019.

The figures published by NHS Digital show the number of patients waiting for an autism assessment is at its highest level since data started to be recorded in April 2019.

It has prompted calls for a "radical rethink" of how autism and ADHD are assessed and treated.

Thea Stein, chief executive of the Nuffield Trust, said: "The extraordinary, unpredicted and unprecedented rise in demand for autism assessments and ADHD treatments have completely overtaken the NHS's capacity to meet them.

"It is frankly impossible to imagine how the system can grow fast enough to fulfil this demand.

"We shouldn't underestimate what this means for children in particular: many schools expect an assessment and formal diagnosis to access support - and children and their families suffer whilst they wait."

Although the National Institute for Health and Care Excellence (NICE) recommends people with suspected autism be diagnosed within three months of a referral, 147,070 patients had been waiting at least 13 weeks in December. This is six times the 24,250 in December 2019.

Analysis of the data by Nuffield Trust found 79% of people who had been waiting 13 weeks or longer had not had their first appointment with a specialist - up from 44% in December 2019.

Between October and December last year, those who had their first appointment waited an average of nine months from referral.

In December 2019, the wait was an average of four months, the thinktank says.

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Ms Stein warned: "We are only now beginning to recognise just how many people are neurodiverse.

"The challenge is that we have an obsolete health service model in place to deal with this avalanche of need.

"The huge rise detailed in our analysis is likely to be down to a combination of changing social attitudes and better awareness.

"We need to urgently understand the different elements of this complex picture and find a whole system approach across education, society at large and the health service.

"Pumping more money into the current model certainly isn't the solution: a radical rethink is required."

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An NHS spokesperson said: "The NHS is fully committed to supporting and improving the lives of those with ADHD and autism which is why we have published new national guidance to help local areas to manage the 50% increase in referrals they have seen over last year.

"NHS England has also begun important work into investigating challenges in ADHD service provision and last month launched a cross sector taskforce alongside government, to help provide a joined-up approach for the growing numbers of people coming forward for support."