The mother of a 17-year-old-boy with autism says her son was punched four times by a police officer while he was at a friend's house in Northampton.
A video has emerged of the alleged attack, which appears to show a police officer repeatedly striking Tristan Perry while another shouts at him to put his hands behind his back.
"We are both very upset by what has happened and we will be taking legal action," the boy's mother, Jodie Lamb, told Politics.co.uk.
"We had just returned from a holiday and I dropped Tristan off at his friend's house. I still don't know why the police were in the boy's bedroom but Tristan was not arrested. My experience of the police has always been very good which is why I am so shocked," she added.
The footage could prove embarrassing for the local police and crime commissioner Adam Simmonds, who enjoyed positive coverage recently due to his reforms to stop and search powers in the county.
Just last week he wrote of the importance of the public having trust in the police, in an article for the website Conservative Home.
When contacted by Politics.co.uk last night, Simmonds said he had only seen still images of the footage but that he had spoken to the chief constable about it.
"I want to know and understand more as soon as possible," he said.
"We have a good record in Northamptonshire with police and public engagement. This is a single event which needs to be understood further and I hope to know more very soon."
In a statement released by Northamptonshire police, assistant chief constable, Rachel Swann said:
"We are aware of a short video circulating on social media allegedly showing Northamptonshire police officers. We take such allegations extremely seriously and immediately referred the matter to our professional standards department as soon as we became aware of it. An investigation is currently underway and as such it would be inappropriate for us to comment further while this takes place."