The education of thousands of pupils with special educational needs is at risk because of the rapid expansion of the academies programme, senior local authority officials have warned.
If significant numbers of "outstanding" schools become academies, councils could lose the ability to provide high-quality SEN services to children in schools that remain under their control, according to the Association of Directors of Children's Services (ADCS).
Local authorities currently retain about 10 per cent of school budgets to provide a range of central services, including admissions and legal support.
But most of the money is spent on expert provision for SEN pupils, including specialist staff who help numerous schools across their area.
Marion Davis, president of the ADCS, said if local authorities lost funding from schools becoming academies, expensive SEN services would be in danger of becoming "unviable".
"If 10 per cent of schools in an area are outstanding and become academies, that is a critical factor about what remains in terms of budget and how you work with schools," Ms Davis said.
"If a significant number of schools convert to academies, there's a real risk that it makes some services that local authorities provide unviable. That's the big risk.
"These are people with qualifications and experience and are not necessarily the cheapest of staff. If those budgets go, there is the danger of having to cut right back on specialist staff that make a vital difference to children's outcomes."
Ms Davis said it was possible that services could be maintained at current levels only if academies choose to buy in their specialist SEN support from councils.
Figures from the beginning of this year showed that more than 220,000 pupils in all schools in England had a SEN statement - about 2.7 per cent of the total.
The Government announced last week that 1,114 schools have expressed interest in becoming academies, of which 626 are "outstanding" and therefore pre-approved after the necessary legislation is passed.
There are currently around 200 academies, which are funded directly by central Government. It is expected that a significant number of schools interested in becoming academies will be motivated by gaining full control of their budgets.
Ms Davis said that in a "worst-case scenario" local authorities could become a "provider of last resort" when academies encounter problems.
"In the rush to improve results, some academies have been keen to get rid of some students," she said. "In that situation, the academies were happy for local authorities to retain responsibility."
Dame Margaret Eaton, chair of the Local Government Association, expressed concern that the expansion of academies could lead to a "two-tier education system".
"Councils will be seeking urgent reassurances that disadvantaged children will not lose out but will benefit from the same opportunities as other pupils," she said.
A spokesperson for the Department for Education said: "All academies have a duty to provide support for pupils with special educational needs as part of their grant contract.
"Funding for those pupils with SEN follows the individual, so no child will miss out. Academies have the freedom to select the support which is most suited to their pupils - sometimes by buying in new, better support and provision, or sometimes using existing local authority services if they are strong.
"Ultimately we trust teachers to know what's best for their pupils."
'Beware going down this route'
More than 50 of the "outstanding" schools that have expressed an interest in becoming academies are special schools, according to figures released last week.
But Lorraine Petersen, pictured, chief executive of the special needs organisation Nasen, said schools should not make the switch.
"If they go down the academy route, they may not be so willing to reach out to mainstream schools," she said.
"I do have concerns about whether special schools fully understand the implications of becoming an academy. A lot of special schools are smaller and more intimate.
"I don't think special schools should become academies - they have a nature to them that doesn't lend itself to going down that route."