Britain's biggest ever policing operation will see SAS units support thousands of police officers during the Queen's state funeral on Monday.
The security operation will draw in at least 2,000 officers from other forces to support the Met's efforts.
A ring of steel is set to be formed around the capital in an operation that will dwarf that of the 2012 Olympics.
Specialist SAS units will be strategically located out of sight around the capital and will only be called upon in the event of an attack.
The late monarch's funeral will see around 500 guests from nearly 200 countries gather at Westminster Abbey.
Former head of royalty protection Dai Davies said in quotes reported by the Daily Mail : “The SAS and those trained in anti-terror quick reaction will also be involved. They will be strategically placed in military barracks and around the capital and will be there as the ultimate line of defence should there be an attack.
“The biggest risk will be the lone wolf or knife attacks from individuals, which are harder to predict. There is always the risk of a car attack too, though there will be barriers that make this more difficult.”
Scotland Yard, who said 34 arrests had already been made “for a range of offences”, did not confirm the number of officers being deployed on Monday.
As well as the logistics of protecting dozens of foreign dignitaries and royalty, hundreds of thousands of people are likely to descend on the capital making for a highly complex security situation.
Police will be divided into high-visibility officers and plain-clothes colleagues who will merge into crowds, while snipers will be deployed on rooftops and thousands of firearms officers will be patrolling the streets of London.
“This will be the largest single policing event that the Met Police has ever undertaken,” Met deputy assistant commissioner Stuart Cundy said.
“As a single event, this is larger than the 2012 Olympics, it is larger than the Platinum Jubilee weekend. The range of officers, police staff and all those supporting the operation is truly immense.”
The public have been asked to act as the force's “eyes and ears” and report anything suspicious immediately.
