The key word is ARMED.
There will be plenty of international security experts there.
And I’d bet some of them will be armed…just not publicly.

Official statements explicitly state otherwise. The Home Office have been open about whether they are authorising foreign bodyguards to carry firearms, e.g Bush at the G8 summit, so why would they now choose to lie publicly and do something different? Foreign heads of state might be allowed a small number of armed bodyguards but they wouldn’t be policing and would be escorted by actual police, in any case they tend to move the head of state away from danger rather than arrest people or engage in gunfights.