Watch: Police issue fines after breaking up rave with 300 revellers
Police handed out more than £15,000 in fines and two officers were left injured after hundreds of people attended two huge parties at the weekend.
Met Police officers found more than 300 people at a venue under a railway arch in Hackney, east London, in the early hours of Sunday.
Police also broke up another large event attended by more than 200 in Knightsbridge on Sunday morning.
Two officers were left injured after crowds became hostile while they broke up the party on Beauchamp Place.
The parties come after a wedding with 400 guests was discovered at a Jewish school in north London.
The Hackney event, which was staged despite the current nationwide lockdown, was reported after residents heard loud music coming from inside the small venue.
Dozens of people attempted to flee after the police arrived by scaling fences and attempting to force open gates.
Officers from the Met said the event's organisers were "uncooperative" and additional resources including police dogs and a helicopter were deployed.
A total of 78 people were stopped and issued with fixed penalty notices to the value of £200 for breaching Covid regulations by attending an illegal gathering - a total of £15,600.
Chief Superintendent Roy Smith, who attended the incident, said: "This was a serious and blatant breach of the public health regulations and the law in relation to unlicensed music events.
"Officers were forced, yet again, to put their own health at risk to deal with a large group of incredibly selfish people who were tightly packed together in a confined space - providing an ideal opportunity for this deadly virus to spread.
"Our frontline officers continue to police this public health crisis with compassion and professionalism but it is completely unacceptable they have to face such needless risks to their own health and to their families too.
"Whilst we will always seek to engage and explain, the message to those who have a total disregard for the safety of others and breach the law so blatantly is clear, our officers will act swiftly and decisively.
"Not just organisers, but all those present at such illegal parties can expect to be issued a fine."
The Met was also forced to break up another large event attended by more than 200 people in Knightsbridge on Sunday morning.
Two police officers were injured after crowds became hostile while they were breaking up a party at the illegal event on Beauchamp Place in Knightsbridge.
Police received reports of a mass gathering taking place in the wealthy neighbourhood at 3.30am on Sunday 17 January.
Several units were deployed to the venue, where they found over 200 people attending an illegal party.
No arrests were made on the night, but 30 fines were issued and a three month closure order is being prepared for the owner of the establishment, the Met said today.
Watch: What you can and can't do during England's third national lockdown