An off-duty policewoman has been punched and kicked on the London Underground after she tried to tackle a suspected fare dodger.
The incident occurred in North London at Wood Green Tube station when a group "attempted to barge through the barrier without tickets".
British Transport Police said the officer also had a drink thrown over her when she challenged the group.
The force has released images of four women and two men.
British Transport Police
|The off-duty policewoman was kicked and punched by a group
British Transport Police
|Detectives said they 'would like to speak to the people pictured'
Detectives said they "would like to speak to the people pictured as they believe they could have information which could help their investigation".
Shadow Justice Secretary Robert Jenrick recently raised concerns about the issue in a viral video of him confronting fare dodgers to "shame people into action".
Jenrick said in a message: "[Mayor of London] Sadiq Khan is driving a proud city into the ground. Lawbreaking is out of control. He's not acting. So, I did.
"It's about the authorities - in this instance, Transport for London (TfL) or the police - not stepping up and not enforcing the rules."
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British Transport Police
|The force has released images of four women and two men
British Transport Police
|The group 'attempted to barge through the barrier without tickets'
TfL said fare evasion is "unacceptable" and that it's expanding its team of investigators to "target the most prolific fare evaders".
At the end of April, TfL announced that more than 500 uniformed officers had been deployed across its network to tackle fare evasion.
Khan said: "Fare evasion is a criminal offence which deprives TfL of thousands of pounds of vital revenue every year that could be reinvested in London's transport network.
"That's why we're expanding our team of professional investigators to cover the whole network and investing in the latest technology to target the worst offenders. It sends a clear message: fare evasion will not be tolerated, and we will hold those who do it to account."
British Transport Police
|Under Said Khan, fare dodging has gone up by 3.8 per cent on the Tube
British Transport Police
|Police say the woman had a drink thrown over her
The year before Khan became mayor, fare evasion on the Tube was at just one per cent, however last year it was 4.8 per cent.
Across the whole TfL network, 3.4 per cent of people fare dodge, costing it £130million per year.
TfL said it is determined to lower the amount of fare dodgers to 1.5 per cent by 2030, while securing a safe, clean and reliable service.
Siwan Hayward, TfL's Director of Security, Policing, and Enforcement, said: "The overwhelming majority of customers pay the correct fare, and it's unfair to those who do that a minority avoid paying.
"We are strengthening our capability to deter and detect fare evaders, ensuring they face the consequences of their actions and that the cost of fare evasion is paid by the evaders, not our fare-paying customers or taxpayers. Fare evasion is not a victimless crime."