Video showed her being held by two male officers during the incident in Croydon on 21 July, while her child could be heard crying in the background.

Police said she had refused to show her ticket to inspectors, a community support officer and constables and "continued to try to walk away".

As the woman's arms were being held, she was heard shouting in the footage "what the hell, what are you doing, what the f*** is going on".

Assistant Commissioner Matt Twist said she was immediately de-arrested and the cuffs removed when it was confirmed she had correctly paid the fare.

He said the child was "comforted" by a police community support officer throughout, but that he regretted any impact it may have had.

The Metropolitan Police said on Monday that it didn't believe officers had acted improperly, but that it was referring itself to the Independent Office for Police Conduct (IOPC) due to the level of "community concern".

The watchdog confirmed on Tuesday that a complaint of racial profiling had been received and said it was assessing the footage.

The woman, who is black, was also allegedly verbally abused by one of the officers.

IOPC director Steve Noonan said: "We know that footage of the woman's arrest has been widely shared on social media and has caused significant community concern, with questions raised about the actions of the police officers involved.

"We have decided that an independent investigation is required to establish the full circumstances, including the actions and decisions made by the MPS officers."

A bus worker called Joe claimed the woman had been abusive when asked to show her ticket.

He told LBC breakfast show host Nick Ferrari: "The inspector told her to please show the pass and she started being abusive to the inspector.

"And when the police asked her to show the pass, she started abusing the police as well. She could have just shown the pass and walked away and that would have been the end of the matter."