Abuse on social media and controversy over investigations by a watchdog have damaged police officers’ confidence so much that the rate of stop and search and arrests has dropped, the head of Britain’s largest force has claimed.

Metropolitan Police Commissioner Sir Mark Rowley told an event in central London that the “growing crisis in confidence” means fewer officers want to take on additional responsibilities such as riot or firearms duties.

Speaking at an event organised by the Police Foundation, Sir Mark said it is “shameful” that officers face abuse online.

“We should be very clear: when people, be they politicians or the public, throw accusations and slurs at the police, they put them in danger by emboldening thugs,” he said.

“Some people won’t care about that – the criminals – but everyone else should.

“I say to all those throwing insults: be very careful which side of the line you are standing.”

He went on: “We police without fear or favour, and for everyone.

“It does no-one any favours for this to be deliberately undermined to drive clicks on social media.

“Worse, we have seen it increasing the violence against officers.”

Chief Inspector of Constabulary Andy Cooke warned last week that police chiefs are being subject to “improper” interference from significant political figures, and that any necessary interventions should be made in private.

Sir Mark said there is “a growing crisis in officers’ confidence to act”, and that the system that holds officers to account has “got out of kilter”.

He cited the case of Pc Paul Fisher, which saw watchdog the Independent Office for Police Conduct heavily criticised for prosecuting the officer for dangerous driving after he crashed on the way to a terror attack in Streatham, south-east London, in February 2020.

Mr Fisher was cleared by a jury nearly four years after he was charged.

“The system that holds officers to account needs to pass the common sense test,” Sir Mark said.

“It should be timely, fair and respected by both officers and the public.

“It isn’t.

“I believe we are seeing the impact of this on our streets.

“Stop and search – an important tactic when used well, which takes knives and weapons off our streets – has declined massively, and the arrest rate in London is also reducing.

“We know that a third of officers say that reduced confidence has led them to voluntarily surrender their public order accreditation, a third say they are giving up their Taser accreditation, and over a quarter their firearms tickets.

“This means fewer officers doing the high-risk jobs we need them to do.

“That risks London becoming less safe.

“Officers should know that when they follow their training and act in good faith, that from their sergeant to their commissioner they will be supported.

“This is the approach in the health service.

“It cannot be right that one part of the public sector – which also makes life and death decisions – should be held to a different standard to others.”