Sir Keir Starmer visited the Met Police’s riots “nerve centre” on Friday and praised officers for keeping the streets of London safe.
The Prime Minister also stressed that far-right thugs plotting disturbances this weekend, and individuals inciting violence online, would face the “full force of the law”.
He emphasised that the Government and police forces across the country remained on “high alert” for any possible disturbances at the weekend, the start of the football season.
Sir Keir told The Standard: “Last weekend, we were all shocked by the horrific scenes of violence that unfolded on our streets.
“A violent mob – led by far-right rioters - set about wreaking maximum destruction and targeting people based on the colour of their skin or who they worship.
“In the days since, we have seen hundreds of arrests, many criminals charged, and some already put behind bars. This is sending a clear warning to all – we will not tolerate violent thuggery.”
He stressed that the whole of the criminal justice system had been “ramped up” to deal with thugs responsible for “horrific scenes”.
The PM added: “This morning, I have been in Lambeth – at the nerve centre of the Metropolitan Police – seeing first-hand the state-of-the-art technology police use to manage major incidents.
“I have heard directly from the officers working around the clock to keep us safe.
“My message to these officers – and to all of our Met Police officers – this government supports you and we thank you for all you do, not just for London but the whole country.”
He stressed further: “We remain on high alert, and we will not let up.
“If you commit a crime on our streets or online, then you will face the full force of the law. The mob does not speak for Britain, and we will keep all our communities safe from this far-right thuggery.”
The Prime Minister has emphasised that swift justice, including sentencing, has been a deterrent to more violent disorder.
Tens of thousands of anti-racism protestors also took to the streets on Wednesday evening, including in Walthamstow, north east London, to oppose dozens of planned far-right demonstrations which failed to materialise.
At least a dozen people were jailed on Thursday for their part in the riots of the past 10 days, with more getting sentences on Friday.
Ryan Wheatley, 40, of Malvern Close, Fair Oak, has pleaded guilty to assault by beating of a police officer at a protest in Southampton on Wednesday.
Jimmy Bailey, 45, of Station Avenue, Ellesmere Port, has pleaded not guilty to a charge of violent disorder at Liverpool Crown Court.
Bailey is accused of being involved in disorder in Paradise Street in Liverpool city centre on Saturday.
Judge Neil Flewitt KC adjourned the case to September 13, when a trial date will be set, and said consideration would be given to grouping defendants together for a trial.
Bailey was remanded in custody.
The Prime Minister chaired his third emergency Cobra meeting on Thursday since the first riot in Southport on July 30.
The riots were partly blamed on false claims that the suspect in the Southport stabbings of three young girls was a Syrian asylum seeker who had come to Britain by “small boat” crossing the Channel and was known to the intelligence and security services.
More cases were due to be heard on Friday at Crown Courts around the country, including Newcastle, Teesside, Liverpool, Sheffield and Inner London.
Scotland Yard officers carried out a series of dawn raids on Thursday to arrest people suspected of being involved in far-right violence in the capital last week.
The Met Police also arrested a man in his 50s in south-east London on suspicion of encouraging murder after a video emerged of a Labour councillor calling for far-right protesters' throats to be "cut".
He had also been arrested for an offence under the Public Order Act following the incident in Kent.
The arrest figure is expected to “continue to rise significantly”, the National Police Chiefs’ Council (NPCC) said.
By Thursday afternoon the total number of arrests stood at 483, it added.
