Sir Keir Starmer has said swift justice, including sentencing, has been a deterrent to more disorder after far-right riots, but that police must stay on "high alert".

The Prime Minister addressed his third emergency Cobra meeting since the first riot in Southport on July 30 and after many planned protests on Wednesday night (August 7) failed to materialise.

Sir Keir,  who is MP for Holborn & St Pancras, told the meeting that police need to remain on “high alert”, the PA news agency said.

He is understood to have said there was no doubt that levels of policing in the right places and swift justice over the past week, including sentencing, have acted as a deterrent to disorder.

Earlier in the day he told reporters that Wednesday night’s events turned out “much better than was expected” and “anybody involving themselves in disorder, whatever they claim as their motive, will feel the full force of the law”.

He said: “It’s important I repeat that because we need to make sure that in the coming days we can give the necessary reassurance to our communities, many of whom – I’ve been talking to some this morning – are very anxious about the situation.”

The Prime Minister's comments came as the final child injured in the Southport stabbings that sparked the riots was discharged from hospital on Thursday.

Her family said they were “deeply saddened" by the recent disorder, including attacks on police, and praised the officers who were first on the scene when the "horrific" events unfolded on July 29.

It has been an “incredibly difficult time for our nation”, they said.

On Thursday the total number of arrests nationally stood at 483.

Many planned events failed to materialise on Wednesday but Gavin Stephens, chairman of the National Police Chiefs' Council (NPCC), warned those intent on violence and destruction "have not gone away”.

Home Office minister Dame Diana Johnson said social media firms have an “obligation” to deal with crimes committed on their platforms.

She said: “If there are criminal offences being committed on social media platforms now, then these social media companies have an obligation now to deal with that.

“If they’re having incitement to violence on their platforms, that needs to be dealt with now, today. We don’t need the Online Safety Act to deal with that.”

Arrests continued throughout Thursday.

The Metropolitan Police 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 on suspicion of an offence under the Public Order Act following the incident in Kent.

A Labour spokesperson confirmed that Ricky Jones, a borough councillor in Dartford, Kent, has been suspended by the party in relation to the video.

Some reporting by PA.