The NSPCC is investigating allegations about how a headteacher and other staff restrained children at Nyland Special School in Swindon.

Two teachers and a teaching assistant, along with head Paul Sunners, were suspended in October over the allegations. One staff member has returned to work this week, but Swindon Council would not say who. The other three are still suspended.

Part of the remit of the children’s charity is to interview children at the school.

The NSPCC Independent Enquiry and Assessment Service (IEAS) investigates cases where abuse has been alleged in organisations or institutions and when allegations are made against more than one person and more than one child is involved.

The specialist team steps in when there would be a perceived conflict of interest if a local authority investigated a case internally. It often investigates abuse alleged against people in ‘positions of trust’.

“I don’t feel the children have been given the answers they deserve,” said a parent who does not wish to be named.

She removed her son from the school over concerns about his welfare and said: “I am very worried that there has not been an outcome.”

A police investigation into the allegations has been dropped.

Phil Baker, secretary of the Swindon branch of the Association of Teachers and Lecturers, said supply staff costs were mounting.

“As an association it is always of great concern when an investigation takes such a long time – not only in terms of monetary costs but also because the children have been deprived of the teachers for six months.

“The average supply teacher can cost up to £170 to £180 per day.”

Nyland School in Nythe teaches children aged five to 11, who have emotional, behavioural and learning difficulties.

A Swindon Council spokeswoman said: “An independent investigation is being carried out by the NSPCC on behalf of the council into allegations made against staff at Nyland School.

“We are unable to comment further until this has been completed.”

She added that the suspended staff were on full pay and temporary cover had been provided.

A Wiltshire police spokeswoman said: “The police investigation into allegations against the four staff members who were suspended in October 2008 was completed in December 2008.

“The four suspended staff were not charged with any offences and no further police action is being taken at this time.”

The NSPCC said it could not comment on its ongoing investigations.