Plans to shake up special educational needs funding could see special units in mainstream schools close, a teaching union says.

The National Association of Head Teachers said reducing the per-place funding for such units from £10,000 to £6,000 a year would be "disastrous".

It also said the plans would not address the wide disparity in funding for children with similar needs.

The government says it has boosted high needs funding by £90m this year.

In its report, Getting it right: Funding pupils with complex needs, the NAHT looks at the impact of the proposed changes to the funding for children with high special educational needs.

The changes include basing the way funds are allocated to local authorities on the number of two- to 18-year-olds in the area.

This will then be modified by three factors - the number of children in bad health or on a disability benefit, low attainment and deprivation levels in the area.

But the NAHT says the proposals do not address the so-called "top up" funding for children with very complex needs, where there are big differences in funding.

The variability in funding levels means children with very similar needs could attract £2,000 of education funding in one local authority but £20,000 in another.

"This is clearly unacceptable and the DfE needs to develop parameters and controls to ensure that funding is fairly distributed within local authorities," the NAHT said.

Kim Johnson, president of NAHT and principal of Bradfields Specialist SEN Academy, chatham, Kent, says: "Those of us who are passionate about the education of children with high and complex needs have been pressing for this review of high needs funding for a long time.

"We desperately need a new approach that creates greater consistency and transparency.

"But we also need to be mindful that local authorities have taken very different approaches and that the transition to such an approach could result in some significant changes."