Restraint should only ever be used when it was “essential to keep a child safe”, and then “for the shortest time possible”, she added.
A police investigation was launched after staff at the Whitefield school discovered a box of USB memory sticks containing 500 hours of CCTV taken inside the padded room between 2014 and 2017.
The investigation ended earlier this year without any charges.
About 40 children with learning disabilities and severe mental disorders were confined for hours in the rooms – typically without food or drink.
Six families of the children involved have agreed for the to show the footage.
The videos show the children in acute distress and many are seen injuring themselves.
Safeguarding expert Elizabeth Swan said it was “easily the worst footage” she had seen.
“You look at the children and they’re being defeated and responding to that treatment with self-injurious behaviour, it’s torture,” she added.
The school’s local MP Conservative Sir Iain Duncan Smith said the “jaw-dropping” footage should lead to “profound change”.
Asked about the footage, the prime minister’s spokesperson said: “The department is looking at the guidance in this space but it is clearly a horrendous case.
“We are clear that this cannot and should not have happened and should not happen again.”
