Covert security tactics will be deployed at the Duke of Edinburgh’s funeral, Thames Valley Police (TVP) said.
Philip is expected to be honoured with a ceremonial royal funeral at St George’s Chapel, Windsor.
A TVP spokesman said: “Thames Valley Police has put in place a wide range of security measures for His Royal Highness’ funeral, some you can see and some you will not be able to see.”
Richard Aitch, director of operations for Mobius International – a firm offering security services for governments and the private sector, said the operation for the funeral will involve “everything that the UK has to offer” and the cost will “run into the millions”.
He told the PA news agency: “It will be an objective to ensure that the security of the service is the maximum possible, but also hidden.
“The last thing they want to do is damage the very feeling and image of the service itself with an overabundance of security.
“There will be numerous covert operatives in the area.”
Mr Aitch said the funeral could be targeted by a range of threats.
“At the lower end you’ve got the cranks and nutters,” he explained. “At the higher end of course you’ve got the terrorism presence.”
The Government Communications Headquarters, also known as GCHQ, will be “listening in on the chatter of what’s going on around the globe”, he said.
The widespread use of facemasks due to the coronavirus pandemic also presents a challenge as they make it harder to identify people, he said.
“Someone can easily hide their face and blend in, so it is a difficult aspect for security,” he commented.
The number of people wanting to pay tribute to the duke could present difficulties for police forces due to England’s ban on gatherings of more than six people or two households.
Police officers on horses stopped crowds forming in front of a sign announcing his death on the railings of Buckingham Palace.