This is the moment a huge crowd of onlookers watched as police arrested several men at a charity book stand in south London.

Dozens of police officers descended on the area surrounding Brixton Tube station just before 6pm on Thursday.

Scotland Yard said the force were in the area with British Transport Police to carry out a pre-planned operation to crackdown on drugs and weapons.

It said Police Community Support Officers were also carrying out work with Lambeth Council’s Trading Standards targeting a number of "unlicensed traders" near to the Underground station.

Video footage emerged of officers involved in a confrontation with a group of charity workers offering books outside the Underground station.

Police involved with the pre-planned drugs and weapons operation were called to assist with the dispute and CS gas was deployed by one of the officers.

Witnesses on social media say the stall belonged to Black Child Promotions, a group which promotes black literature.

On its Facebook page, the group is described as a pan Africanist organisation promoting black education and knowledge in the community.

Clips of the incident posted on Facebook and Twitter have sparked criticism of the police for being too heavy handed.

One video posted online appeared to show a dispute between a police officer and one of the men running the stall.

He explains to the police officer that he is not selling books and that if someone wants to leave a donation in their charity box “that’s up to them.”

Several other clips, which are believed to have been filmed a short time later, show a struggle and loud shouts from the crowd as police arrest the men.

A Met Police spokesman said in a statement: “Plain clothes officers from the Met and British Transport Police (BTP) were already in the area conducting an unrelated, pre-planned operation targeting those involved in criminality in and around Brixton tube station.

“They attended the scene along with uniformed officers from BTP. CS spray was deployed by one of the uniformed BTP officers.

“Two men were subsequently arrested for obstruction - they remain in custody.

“Due to the large number of people who had gathered at the location, further officers attended the scene to manage the crowd.

“There was one further arrest for a public order offence.”

The spokesman added that senior officers in the Lambeth borough had reviewed the incident with officials at Lambeth Council.

Police initially said one of the men was arrested on suspicion of assaulting an officer.