UK police officer caught on camera punching grandmother to the ground

An investigation is underway after a UK police officer was caught on camera punching a grandmother to the ground.

Video of the incident was uploaded to social media, the Manchester Evening News reported. In it, a man is seen being held on the ground by police officers outside an Oldham supermarket.

The man's mother then yells at the officers - urging them to "stop hurting my son", sister and witness Danielle Willisford told the MEN. That's when the video shows the officer lashing out and punching her to the ground.  

"My mum did not deserve that at all," Willisford told the newspaper. "It shouldn't be like that."

Willisford's mum received a black eye but wasn't seriously injured.

Police told the MEN in a statement the man was being arrested for drunken disorderly.

"At the time of his arrest a crowd had gathered and footage of the incident has been uploaded onto social media," a Greater Manchester Police spokesperson said.

"The incident has been referred to our professional standards department, who will review the body-worn video of events leading up to the arrest, along with the footage posted."