Lawyer Aamer Anwar, rector of Glasgow University, said: “Public gatherings of only 2, some of us haven’t seen our parents in weeks, our children not at schools, nearly 14,000 dead as @metpoliceuk allow this madness on Westminster Bridge.”

Former police officer Mark Williams-Thomas, now an investigative journalist, tweeted: “This makes me so angry - breaks all the rules . What's the point of having rules and lockdown if police and public break them.”

Another contrasted the police use of drones to pursue dog walkers and crackdowns on park exercising with officers now “herding hundreds of strangers in tube train proximity on Westminster Bridge to thank NHS staff (while making their job more difficult).” Even Ben Stokes, England’s star cricketer, waded in on twitter: “Let go to the bridge tonight and clap with loads of other people to show our support for the NHS, it’s fine if we put other people at risk as long as we get seen on camera clapping I’m cool with it” SERIOUSLY.”

One woman bluntly tweeted: “Met Police Chief Cressida Dick was on Westminster Bridge last night and did nothing. Dick is the right name!”

Asked about the event on LBC, Sadiq Khan, London’s mayor who is responsible for the Met Police, said he was concerned that rules “appeared not to be observed” and believed the Met and ambulance service would be “asking questions” over how it was allowed to happen.

“Clearly the advice does not appear to have been followed. A number of people were not 2 metres apart and these rules are there for all of our wellbeing and health,” he said.

“We have to be cognisant of the facts that when this goes into social media people can get the wrong impression but also risk personal health so I am sure there will be questions.”

A more orderly and smaller version of the Thursday night “clapping” for carers and NHS staff was staged the previous week. It is an event that is replicated in Europe and in the United States, where police and fire vehicles flash their lights in unison across states to thank their health staff.

Asked who had authorised it, the Met said: This wasn’t an organised event as such so no ‘authorisation’; Westminster Bridge is straddled by New Scotland Yard and St Thomas’s Hospital so naturally a bit of central and visible point of focus for the emergency services.

“In terms of moving people on, each instance is assessed by officers present. In this instance no one was moved on.”