False claims that the perpetrator was an asylum seeker spread quickly on platforms including X, helped along by fake news sites and bots linked to hostile foreign states including Russia.
This storm of disinformation triggered warnings from Sir Keir, who said anyone “whipping up violence online will face the full force of the law”.
Media regulator Ofcom, which has been in discussions with social media platforms about their approach to tackling disinformation, urged the companies to “act now” to take down harmful content.
Yet ultimately, politicians and regulators have little more than tough words at their disposal.
Under new online safety laws, Ofcom will be granted powers to fine tech giants up to 10pc of their global turnover if they do not do enough to remove harmful material from their platforms.
But these laws are not due to come into effect until next spring, leaving UK authorities in limbo.
“Escalating tensions will lead to repeated calls for the act to be implemented as quickly as possible,” says tech analyst Paolo Pescatore. “It seems ludicrous that this is taking so long, more so with enforcement not expected until early next year.”
What’s more, there are mounting concerns that the laws do not go far enough in policing online material – effectively giving Silicon Valley a free ride.
Ian Russell, whose daughter Molly took her own life after viewing thousands of images on social media promoting suicide and self-harm, is among campaigners calling for the rules to be strengthened.
One of the key points of contention is the removal of proposals for controls on material that is “legal but harmful”. The wording sparked concerns of an incursion on free speech, but critics say the U-turn amounts to a watering down of the rules.
“These original proposals were too far-reaching and did have the potential of incentivising platforms to limit free speech online,” says Niamh Burns at Enders Analysis. “But it could be argued disinformation has slightly fallen through the cracks in the end.”
Sir Keir hinted the Government could review the act, saying ministers will have to “look more broadly” at social media rules in the wake of the riots.
But as the laws grind their way through British bureaucracy, does Sir Keir have other options for taking on the might of big tech?
One relatively straightforward response would be to haul Musk in front of a select committee.
This form of public pressure would be particularly fitting given the Tesla tycoon has repeatedly waded into the debate – and even been guilty of spreading disinformation himself.
The billionaire this week shared an image of a doctored Telegraph headline that appeared to suggest rioters would be sent to detainment camps in the Falklands. Musk took down the post, but not before it had been seen more than 2m times.