The home secretary and the Police Federation have condemned a video which shows an officer on the ground being punched and kicked.
Video circulating on social media shows an officer struggling with a man in Frampton Park Road in Hackney, north London.
The footage was branded “sickening” by Priti Patel, while the federation said: “We are not society’s punch bags.”
Two men, aged 20 and 38, were arrested on suspicion of assault on police.
The officers, a man and a woman, suffered minor injuries but did not require hospital treatment, the Met Police said.
A member of the public, who had claimed to have been assaulted, flagged down the police on Wednesday afternoon.
In a statement, the Met said: “As an officer attempted to speak with those involved, one of the men resisted and a struggle ensued. A number of other people became involved whilst the officer was on the ground.”
Footage appears to show the officer trying to restrain a man but they then fall to the ground with the officer pinned underneath.
Passers-by began filming and taking selfies as the officer and the suspect grappled.
The female officer attempted to keep people away from the scene and also suffered injuries before more officers arrived and arrested the two men currently in custody.
Ken Marsh, chairman of the Metropolitan Police Federation, said: “Yet again this starkly shows the dangers [officers] face and the bravery they show each and every day keeping Londoners safe.
“We are not society’s punchbags. We have families we want to go home to at the end of every shift, but the dangers are stark and seemingly escalating.”
Supt Martin Rolston said: “This incident, which was captured on someone’s mobile phone is truly shocking.
“My officers went to the assistance of a member of the public – who asked for their help – after stating that they had been assaulted.
“What happened next is a reminder of the risks our officers take whilst going about their duties.”
By BBC London Home Affairs correspondent Katharine Carpenter
The context surrounding the incident in Hackney still isn’t clear, the Met says the officers were responding to a request for help but we don’t yet know how that led to a struggle on the ground.
I understand police in Hackney had already planned to meet with local community groups today, now this incident and the tensions surrounding it look likely to dominate the conversation.
Most recent Home Office figures show there were nearly 5,000 attacks on Met Police officers and just under half resulted in injury.
But there has been concern that anti-police feelings expressed during the recent Black Lives Matter demonstrations might see that number rise.
Home Secretary Priti Patel tweeted: “Sickening, shocking & disgraceful.
“My thoughts are with the outstanding officers who were subject to this disgusting violent attack.”
Mayor of London Sadiq Khan said: “I utterly condemn the disgraceful attack on two Metropolitan Police officers this afternoon.
“These brave officers were doing their duty and assisting the public. We owe them a debt of gratitude.”