She is always accompanied by officers from SO14, the Metropolitan Police's Royalty Protection Branch, who will be backed up by a large number of uniformed officers, as well as plain-clothed officers, armed police on the ground and marksmen on rooftops.
Dai Davies, a former head of Royal Protection, said the level of security would be decided by the available intelligence on the threat level to the Queen.
He said: "Security is always arranged in layers, starting with the close protection bodyguards and then in concentric rings, like an onion skin. Additional layers will be added as appropriate, according to the intelligence available.
"As far as I'm aware there is no specific threat to the Queen but you can never rule out so-called fixated individuals, and that could include individuals inspired by Isil.
"There will have been huge resources put into making sure the venues are safe and secure, because you want to prevent an attack happening in the first place.
"But the greatest danger always lies in the travel to and from these engagements, and that is why I can never understand why Buckingham Palace publicise the dates and venues so far in advance.
"Queen Victoria was the target of assassination attempts while she was travelling in her carriage, so we have known this for a long time.
"That said, the Queen has always taken the view that she is not going to be put off by any kind of perceived threat and at the end of the day you cannot give 100 per cent protection, but the Met are so well used to doing this sort of thing now that they will take the appropriate steps in conjunction with Police Scotland."
The Queen overtakes Victoria's record reign of 63 years 216 days today.
- Daily Telegraph
