The group of four activists were accused of breaking into the Elbit Systems factory near Bristol.
The Princess of Wales will go to Italy next week on her first official overseas engagement for more than three years.
The director of public prosecutions has told prosecutors in England and Wales to bring charges more quickly.
Police officers are treating the death of Jo Shaw as a homicide.
The PM hosts a summit of leaders from the police, arts and universities, after a spate of attacks against British Jews.