Henry Shelford, the chief executive of ADHD UK, told The Guardian the minimum waits were ‘heartless and dangerous'.

The newspaper said four ICBs had imposed two-year minimum waits with 15 ICBs introducing ways of rationing assessments for ADHD and autism to try to balance their books.

West Yorkshire NHS ICB has introduced a minimum waiting time of two years from referral, while North East and North Cumbria ICB has a 78-week minimum waiting time for an initial assessment.

Rebecca Gray, director of The NHS Alliance's mental health network, said the need to balance budgets and the pressures of soaring demand had in some places had led to "minimum waits" or even the closure of some waiting lists.

‘The current situation is unsustainable and delivers a bad deal for patients and taxpayers,' Gray said.

‘That so many people feel they will not get the support they or their child needs without an assessment reflects broader challenges across education, health and employment.

‘But there are immediate steps that can help. A national tariff and service specification for ADHD and autism would remove the risk of chaos in the market, improve the quality and consistency of services for patients and ensure the NHS can use its resources more effectively.'

A Government spokesperson said: ‘Last December, we asked clinical psychologist Professor Peter Fonagy to lead an independent review, examining the prevalence of - and support for - ADHD, autism, and mental health conditions. Professor Fonagy's final report will be published shortly, and will inform our new national approach in this area.'