A massive security operation was being ramped up today as final rehearsals were taking place for the Coronation of King Charles.

A ring of steel was being put in place around Westminster Abbey, with roads closed off, to counter any threat from protesters or terror groups.

Thousands of police will be deployed to protect the procession and ceremony on Saturday, which will be attended by heads of state and government leaders. As London was set to “showcase” Britain on the global stage:

•The first glimpses of the Coronation were revealed as rehearsals took place in central London in the early hours of today.

•Hundreds of soldiers, many on horseback, went from Buckingham Palace, past Trafalgar Square and Downing Street, to the abbey.

•The Diamond Jubilee State Coach and Gold State Coach were taken down The Mall.

Security minister Tom Tugendhat said the security operation was one of the “most important”. It followed a security alert last night when a man was arrested outside Buckingham Palace after shotgun cartridges were allegedly thrown into the grounds.

MI5 and the intelligence services, MI6 and the GCHQ spy listening centre, are involved in identifying any threats, including possibly from overseas.

Ministers stated that controversial new public order laws would target “guerrilla tactics” of climate activists blocking roads in the capital.

The Bishop of London, Dame Sarah Mullally, told of the “privilege of a lifetime” to be one of the first female church leaders to take part in a coronation.

Across the country, community and other groups were planning hundreds of street parties to join in the coronation festivities.

King Charles III leaving Westminster Abbey following a rehearsal for his coronation

The Met Police operation, known as Golden Orb, will be one of the most significant and largest security operations the Met has led.

There will be more than 29,000 police officer deployments over the coming week in the lead up to Coronation Day and over the rest of the Bank Holiday weekend.The Met said 11,500 officers would be on duty on the day of the Coronation and that the police wanted to ensure that the public enjoyed a “spectacular celebration”.

It said the force had been preparing for months to keep people safe from any threats, but urged the public to report suspicious activity.

It added that deployments would include “officers lining the processional route, managing crowds and road closures, protecting high-profile individuals, and carrying out searches with specialist teams” and that “officers from our dog unit, firearms unit, marine support, and special constabulary” would also be “ready to respond to any incident or crime”.

Police outside Buckingham Palace

It said it intended to use facial recognition technology in central London. A spokesman said “The watch list will be focused on those whose attendance on Coronation Day would raise public protection concerns, including those wanted for offences or have an outstanding warrant for arrest issued by the courts, or those under relevant offender management programmes in order to keep the public safe.”

Deputy assistant commissioner Ade Adelekan, the officer in charge of the operation, added: “We want Londoners and visitors coming to the city to enjoy this historic and momentous occasion safely and securely. On Coronation Day we will have the largest one-day mobilisation of officers seen in decades with just over 11,500 officers on duty.

“The weekend promises to be a spectacular celebration and the Met police is honoured to be policing such an internationally-important event right across the capital.” Shortly after midnight, the Diamond Jubilee State Coach was accompanied by hundreds of soldiers as it travelled along The Mall, in a rehearsal of the procession.

A police sniffer dog at the scene outside Buckingham Palace

Royal fans waited for over three hours for the parade to make a return journey down The Mall. Hundreds from the Army, Navy and RAF marched through central London before stopping along Whitehall and standing in silence.

Drums were only played by marching soldiers when they returned down The Mall after 3am. The rehearsal had particular poignancy given that just months ago, the funeral procession of Queen Elizabeth had taken a very similar route. The parade began when a brass band on horseback practised as they accompanied the coach as it passed through Westminster. Soldiers from a wide variety of regiments marched down The Mall after 1am.

Other soldiers were spotted parading in Parliament Square and practised changing position as Big Ben chimed.

Artillery regiments rehearsed moving cannons on horseback and soldiers were seen pretending to fire them.

The procession returned to Buckingham Palace shortly after 3am with the bands in full swing.

The Gold State Coach was spotted passing Buckingham Palace shortly after 3.20am.

Prince Louis and the Prince of Wales leaving Westminster Abbey

Mr Tugendhat stressed that police were “all over” the huge security operation. He told Times Radio: “What we have been planning for a number of months now is one of the most important security operations that the country has put into plan.

“This Coronation is not just an opportunity to celebrate our new King but also an opportunity to showcase the UK to the world.” But he also suggested that groups or individuals may also have been plotting for months to try to disrupt the Coronation. At least 15 tents are already positioned along The Mall and royal fans got to test their viewpoint as they camped out.”