Protesters who try to disrupt the coronation can expect “very swift action” from the Met who will have “an extremely low threshold" when dealing with them, the force has vowed.

Deputy Assistant Commissioner Ade Adelekan pledged the force will not tolerate any criminal activity camouflaged as protest during the event, set to be watched by millions.

A mammoth security operation is underway that will see 11,500 police officers on duty on Saturday and 10,000 military personnel taking part in the ceremony.

Specialist teams have begun scouring areas of central London where events will unfold and will continue monitoring crowds to spot signs of suspicious behaviour.

The plan, dubbed Operation Golden Orb, has been re-examined after a security incident outside Buckingham Palace on Tuesday evening when a man who allegedly had a knife threw shotgun cartridges over the palace gates.

The alert prompted a “suspicious” bag to be blown up in a controlled detonation while the man was detained. The incident is not thought to be terror-related.

Mr Adelekan said the security plan had been reviewed in the wake of the incident to make sure there are “no gaps”.

He said: “We’re absolutely confident that we’ve got a plan that will deliver the coronation in such a manner that everyone will come to London and celebrate and there will be no issues whatsoever.”

Asked about how officers will deal with protesters, he said: “Our priority is around safety and security for everyone that’s going to come to this event, and we want to make sure that everyone enjoys it.

“We have an extremely low threshold for anybody or anything that will disrupt this event and what you will see is very swift action from us."

Among the force’s security protocols for the Coronation is the use of facial recognition technology across central London.

Scotland Yard said its watchlist “those whose attendance on Coronation Day would raise public protection concerns”.

It comes as new laws to curb protests came into force on Wednesday ahead of Saturday’s historic ceremony.

Under the new Public Order Act, protesters who block roads will face up to 12 months behind bars.

King Charles III leaving Westminster Abbey in central London, following a rehearsal on Wednesday for his coronation

An official letter warning of the new powers was sent to anti-monarchy group Republic, which said its campaign around the coronation will proceed as planned.

Republic boss Graham Smith said it is “very odd" the letter came from the Home Office and described it as “intimidatory".

He told the PA news agency: “We’ve been liaising closely with the police about the protest for weeks. We’ve had meetings with them.

“They’ve said very clearly that they have no problems with our plans. I just can’t understand why the Home Office thinks it’s appropriate to send a letter like that, which was anonymous in terms of no person’s name on it.”

He said there are plans for 1,700 people to protest in Trafalgar Square on Saturday.

Hundreds of thousands of people are expected to travel to central London for the event, including scores of foreign VIPs who need close protection.

Commander Karen Findlay, who is Gold Command for the policing operation, said there are more VIPs for the coronation than there were for the Queen’s funeral.

She described it as an “historic, unprecedented mobilisation” for police in terms of scale.

“It’s such an event of constitutional, spiritual importance for us all to be involved in,” she said.

A total of 29,000 officer shifts will be used during the days around the coronation, with specialist teams including armed police, sniffer dogs, mounted officers and marine officers on the Thames all taking part.

There will be an airspace restriction across London on Friday and Saturday as part of the “extensive” security preparations.