A third of local authorities face a shortage of dyslexia teachers, a literacy charity has warned, adding that an official pledge to improve funding for the specialists has been left “in tatters”.

In 2009, then schools secretary Ed Balls pledged to spend £10 million on training 4,000 teachers to become dyslexia specialists, to ensure that all pupils who needed it had access to support.

But research by the Driver Youth Trust found that, almost a decade later, the government has only spent half the allocated funds and trained 3,000 specialists.

And, according to a freedom of information request by the charity, the Department for Education has not collated data on where they reside or the work they do.

“It has long been clear that children who struggle with reading and writing require specialist support,” said Jules Daulby, director of education at Driver Youth Trust.

“It is concerning that authorities across the country do not have an adequate supply of specialists,” she added in a statement that described the legacy of the government’s funding pledge as being “in tatters”.

The data, released to coincide with Dyslexia Awareness Week, adds to concerns that teachers are not being properly equipped to help children with special educational needs.

About 10 per cent of the population, or an average of three children in every classroom in the UK, are thought to have dyslexia.

Research from the Driver Youth Trust, released last week, suggested that support for students with special educational needs varies dramatically across England.

A child in inner London is 50 per cent more likely to get sufficient support to sound out words as they learn to read than in the North West, East or Midlands, it found.

In Scotland, thousands of children with additional support needs (ASN) are also not getting the specialist support they need.

A recent study by the Scottish Children’s Services Coalition found that while the number of pupils identified as having ASN rose by more than half from 2012-17, the number of specialist support staff increased by only 6 per cent.

In Scotland, the definition of ASN includes dyslexia, as well as mental health problems, ADHD, autism spectrum disorder and those with experience of the care system.