More than 500 people attended a rave in a Norfolk forest on the weekend new lockdown measures over illegal gatherings came in to force.
Since Friday police in England have been able to fine organisers of illegal gatherings of more than 30 people – such as raves – up to £10,000.
Police said the unlicensed music event had been going on in Thetford Forest since about 23:20 BST Saturday.
Officers eventually closed down the rave at 18:30 on Sunday.
Elsewhere, police attended events in Leeds, Essex and the West Midlands, while Piers Corbyn, the brother of former Labour Party leader Jeremy Corbyn, was given a fine for holding an anti-lockdown protest in Trafalgar Square in central London on Saturday.
After a member of the public reported large numbers of cars queuing to access a fire route, police found the Thetford Forest event near the English Heritage site Grimes Graves.
Paramedics were called after reports a man had become unwell.
Assistant Chief Constable Nick Davison said it was “clear this is a well-established and planned event” which was due to go on until Monday.
“Due to the number of people in attendance, we needed specialist teams to enter the site to close it down. Officers trained in public order, experienced in dealing with such events, entered the site and turned the music off at around 6.30pm.
“I would like to thank local residents for their patience and understanding while we brought this to an end.
“Due to the nature of the location and numbers of people in attendance, this was a challenging event to disrupt and required mutual aid from other forces which takes time to arrange.
“Officers did meet some hostility when entering the site with bottles and cans used as missiles and thrown at officers. Fortunately, no-one was injured.”
West Yorkshire Police said eight people were fined £10,000 for holding parties in the Headingley and Burley areas of Leeds, including two DJs at a party. Equipment was also seized.
The force said a 27-year-old man from Lincoln had been charged with causing a public nuisance after a gathering on Wepener Mount, Harehills, on Saturday.
Supt Chris Bowen said officers “hope people will recognise the ongoing risks of holding or taking part in events such as this”.
In London, the Met Police issued a £10,000 fine to Piers Corbyn for holding an illegal gathering in Trafalgar Square.
The 73-year-old confirmed the fine and his arrest to the PA news agency, adding: “We’re going to refuse to pay and appeal the process.”
In a tweet, Mr Corbyn called the demonstration an “epic success”.
Meanwhile, the Met said it was also considering a similar fine for four people in relation to an unlicensed music event in Hackney Wick, east London.
Police in Harlow, Essex, seized thousands of pounds worth of equipment ahead of an unlicensed music event on Saturday afternoon.
Ch Insp Lewis Basford said the force would be “looking to identify the organiser and take them to court”.
He added: “My final message is to the organisers: we will seize the equipment – I don’t care if you’ve hired it from someone or if it’s yours, we will break up your event, and we can now fine you up to £10,000.”
West Midlands Police said it had dealt with about 90 reports of possible breaches of restrictions, but had not had to use its enforcement powers.
Home Secretary Priti Patel has said the new legislation represents a crackdown on “the most serious breaches of social distancing restrictions”.
But Metropolitan Police Federation chairman Ken Marsh said the it will mean “absolutely nothing” in terms of enforcement in London.
“People just set up a music box in the middle of the street and say ‘it’s not mine’ – it’s utter nonsense,” he said.