MI5 – standing for “Military Intelligence” – is known for its intense work. However, it’s not known for being intelligent in other ways. A hilarious example is staff.
It’s usually the case Journalists for example are mistaken for spies. They’re approached for updates but can’t provide any.
It sometimes turns nasty. There are stories of Journalist’s being harassed for contact. It lasts years and friends have to help out.
In other cases teachers are falsely arrested for spying for States overseas. It’s not true but they get on with it anyway.
The idea of knowing your own staff isn’t a settled issue in any MI5 office. It’s so bad in some places they’ve got to reorganise to remember who someone is.