Police were "kicked and punched" with dozens injured as up to 150,000 people gathered for Tommy Robinson's rally in central London with some officers left with "broken teeth, a possible broken nose, a concussion, prolapsed disc and a head injury'.
The Metropolitan Police have indicated its operation "is drawing down after a very challenging day" which saw "disorder (and) violence" directed at officers - leaving 26 injured.
It also saw "25 arrests made so far", however, the Met Police believe "it is just the start".
Mr Robinson, whose real name is Stephen Yaxley-Lennon, organised the 'United the Kingdom' event which police estimate between 110,000 to 150,000 attended - "significantly exceeding the estimates of organisers".
Many of the supporters gathered on Whitehall, where a series of speeches from Mr Robinson, Katie Hopkins, Laurence Fox and Elon Musk - via video - were heard.
A counter-protest held by Stand Up To Racism - which the Met estimate about 5,000 attended - was organised nearby.
"While both protests began largely without incident, it is deeply regrettable that a number of those who were part of the ‘Unite the Kingdom’ protest became involved in disorder in multiple locations," the Met said in a statement.
"There was insufficient space to fit them all in Whitehall and Parliament Square, with crowds backing up onto Bridge Street and Westminster Bridge."
Police blocking protesters with shields
|MET POLICE
The Met said it meant "a number of people turned off onto Victoria Embankment to get out of the crowds which was understandable".
"However, we then saw large crowds ignore police directions, turning left up Horse Guards Avenue, Whitehall Place, Northumberland Avenue and Craven Street in an effort to get into Whitehall, including into sterile areas and areas occupied by those taking part in the Stand Up To Racism protest," the Met added.
As officers intervened "to block their path" some were assaulted with "kicks and punches".
"Bottles, flares and other projectiles were also thrown and concerted attempts to get past barriers were made," the Met stated.
Police officers arrest a protester during the Tommy Robinson-led Unite the Kingdom march and rally
|PA
"Officers had to put on full protective equipment and in a number of places had to use shields. Horses and dogs were also used to keep the Unite the Kingdom protesters away from opposing groups."
The Met said that on top of the "violence", protesters scaled fencing and scaffolding around Whitehall, "climbing to height putting themselves and others in danger".
About 7.30pm, 25 arrests had been made for offences, including affray, violent disorder, assaults and criminal damage.
Met Assistant Commissioner Matt Twist said officers knew it "would be busy and potentially challenging".
"They policed without fear or favour and approached engagement with all protesters positively," Mr Twist said.
"There is no doubt that many came to exercise their lawful right to protest, but there were many who came intent on violence.
"They confronted officers, engaging in physical and verbal abuse and making a determined effort to breach cordons in place to keep everyone safe."
Mr Twist said the "violence they faced was wholly unacceptable" as 26 officers "were injured".
"Including four seriously - among them broken teeth, a possible broken nose, a concussion, a prolapsed disc and a head injury," he added.
"The 25 arrests we have made so far is just the start.
"Our post-event investigation has already begun - we are identifying those who were involved in the disorder and they can expect to face robust police action in the coming days and weeks."
Mr Twist concluded that he was "hugely grateful to the officers who were deployed in central London today".
"To those on duty in all 32 boroughs responding to 999 calls and to the more than 500 colleagues from forces across England and Wales who stood alongside us in some very challenging circumstances," he said.
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