The Met received an allegation earlier this month that a number of officers had their hair cut while at Bethnal Green police station on 17 January.
A local investigation concluded that 31 police officers should face a £200 fixed penalty notice fine over the incident, while two officers who were involved in organising it have been put under investigation for misconduct.
“Although officers donated money to charity as part of the haircut, this does not excuse them from what was a very poor decision. I expect a lot more of them.
“It is right therefore, officers should each face a £200 fine, as well as misconduct action for those two who organised this event.”
Mr Barnett added that it was also right for the public to expect officers to be “role models” in following the restrictions.
“I hope this action proves that police are not immune to enforcement of the rules, and we are prepared as an organisation to take action if we see officers have behaved irresponsibly,” he said.
The officers were photographed in uniform at the cafe by a member of the public who alerted the Met to the breach.
A subsequent investigation led to all of the officers involved being ordered to pay £200 each over the incident.
Chief superintendent Rob Atkin, South East BCU commander, said that those involved had “fallen short” of the standard expected of them and failed to set an example to the public on following the rules.
“It is right that they will pay a financial penalty and that they will be asked to reflect on their choices,” Mr Atkin added.