Around 100 people attended an unlicensed music event on a patch of empty land in Stanford-le-Hope, Essex on Saturday night.
Officers seized music equipment and are still looking for those who fled so they can be issued with COVID fines.
Meanwhile in Edinburgh, three people were arrested for anti-social behaviour and a serious assault after "hundreds" gathered at The Meadows in the city centre on Saturday.
A 22-year-old man was attacked and a 17-year-old boy seriously injured over the course of the evening.
Condemning the gathering, Chief Inspector Sarah Taylor from Police Scotland described the events as "blatant anti-social behaviour".
"Officers were called to a number of incidents over the course of the day," she said. "Hundreds of people were moved on or dispersed from the area.
"Three people have so far been charged in connection with anti-social behaviour and a serious assault, and we are working to trace others involved in various incidents."
Coronavirus fines of £10,000 are given to people proved to have organised a large-scale illegal gathering during lockdown.
People who break the rules are fined £200, doubling for every repeat offence up to £4,600.
Officers were also scrambled to a large gathering in the village of Dorstone in Herefordshire at around 1am on Sunday.
A "number" of arrests were made for driving offences, West Mercia Police said.
Dozens of people were told to leave the site and a Section 63 dispersal order was put in place, the force added.
Reports were also made about a planned lockdown event in Sevenoaks, Kent, on Saturday.
Police attended to find large groups of people in the area. The music equipment was then seized and people were ordered to go home.
Superintendent Simon Thompson, from Kent Police, warned against people planning further events on Monday.
"We appreciate that lockdown has been tough for everyone and over the long Bank Holiday weekend people may be tempted to attend these events but I must be clear that Kent is not open for unlicensed music events," he said.
"As our officers have shown, we will move people on who come to Kent for this reason, seek to prosecute the organisers and seize equipment that they may bring with them.
"We want people to have fun and enjoy themselves but not at the expense of others in the community."