A police officer was injured during clashes with youths after Eid celebrations in east London, as police leaders warned they had been given little time to prepare to enforce new social distancing restrictions.
Violence broke out in Ilford after police asked a crowd to disperse.
The Metropolitan Police said that as a crowd of around 150-200 people who had attended Eid celebrations began to leave the area, a fight broke out between two groups.
One officer suffered a head injury after police intervened to separate the groups. His injuries are not believed to be serious.
A man was arrested on suspicion of a public order offence and assault of an emergency worker.
The east London disturbances, at 11.30pm on Thursday, came within hours of the Government imposing new restrictions banning families in different households from meeting each other in a swathe of communities across the north west, following a spike in Covid-19 infections.
The restrictions will impact on thousands of Muslim families who had been preparing to celebrate Eid in towns such as Bradford, Blackburn and Greater Manchester, and have been likened to banning Christmas.
Muslim leaders called on their communities to continue exercise responsibility and follow social distancing rules (see pictures below).
But many also expressed frustration, both at the short notice of the new restrictions and the fact people are still being allowed to gather at pubs and beauty spots across the region.
Crowds were pictured ignoring social distancing at pubs in Manchester on Friday, despite the government ruling that residents should not meet members of other households.
Police leaders also criticised ministers for giving them little warning about the new restrictions, leaving forces unable to plan for enforcement measures.
Brian Booth, the chairman of West Yorkshire Police Federation, said: "Yet again we are struggling to police - and get to grips with - what can only be described as haphazard announcements made by the Government in relation to tighter Covid-19 restrictions.
"It is an absolute nonsense that we as the police service have not been afforded the time to put things in place prior to an announcement.”
He added: "Many people in Kirklees, Calderdale and Bradford will have woken up to the news that they are subject to tighter restrictions on their lives. And it will be up to my colleagues to police these restrictions.
"We must also remember that a lot of the areas subject to lockdown have communities who would have been intending to celebrate Eid and who will now be disappointed by this announcement. And it will be our West Yorkshire Police colleagues who will now be on the front line of having to manage the situation and stop separate households from meeting each other at their homes.”
Following the disturbance in Ilford, Ch Supt Stephen Clayman, leading the Met’s East Area Command, said: “While we accept that celebrations take place, and we have no desire to spoil them for the community, if they descend into violence we absolutely will step in.
“While we appreciate this is a time of excitement and celebration for some, the sight and sound of such a large group was concerning and even distressing for others.”
The leader of Redbridge Council, Councillor Jas Athwal, added: “We want people to enjoy the summertime and especially times of celebration both safely and peacefully. We certainly don’t want to see a repeat of the scenes that marred Ilford Lane last night.
“Gathering in large groups is not safe for individuals, their friends or their family members who they may end up inadvertently infecting with the virus.”
Ilford South MP Sam Tarry condemned the incident as “unacceptable”, adding: “There can be absolutely no excuse given for such behaviour on our streets, even more so during a pandemic.”
There has been widespread frustration at the sight of people gathering in large numbers on beaches in southern England, while at the same time people in northern cities were banned from gathering with family members.
Tallha Abdulrazaq, an academic at the University of Exeter specialising in counter-terrorism and security, wrote: “Be a drunken t***** and get blasted by the sun on a beach this weekend! Just don't even think about visiting your parents on Eid if you're a Muslim living in the North.”
Adam Wilkinson, Lead Member Children & Young Peoples Services at Calderdale council, hit back at suggestions by some MPs, including Calder Valley Conservative MP Craig Whittaker, that BAME people were to blame for a spike of cases in Greater Manchester, Bradford, Oldham and other northern towns by not taking the pandemic seriously.
He said: “This is unfair and hurtful, especially when today is Eid. If Craig thinks this is a BAME problem he must not have seen reports of raves in Manchester, football celebrations, VE day gatherings, packed pubs & crowds on beaches. This is just scapegoating & an MP should know better.”
As sunseekers flocked to beaches along the south coast on Friday, with temperatures hitting 37.8C, several stretches of coast were marked as red on council social media apps designed to help social distancing.
By mid afternoon, nearly all of the seven-mile stretch of beach between Poole Harbour and Highcliffe was marked as red on the council's beach app, meaning "avoid, safe social distancing not possible".
There were also large crowds at Brighton beach, Bournemouth and Thanet in Kent.
Yvonne Jones, 66, who has been a beach hut holder in Poole for 35 years, said: "There shouldn't be this many people here - but Boris [Johnson] should have made sure people stayed in their own counties."