Here's my theory and how I arrived at it:
Since Makepeace asked for it and the Staff out of all the treasures in Gladstone's crypt, it might be the most powerful artifact in there (with the exception of the Staff itself, of course). The question is, what did Gladstone use it for? His Cloak of State... he'd probably have worn it on formal occasions, as when addressing Parliament or giving a speech... situations in which he'd want to persuade people of his point of view. I think it was infused with extremely strong Charm and Glamour spells to captivate his audience, turning magicians into fawning boot-lickers and commoners into adoring sheep. Of course, this is all speculation, as there's no canon evidence one way or the other, but it seems to make sense... what do you think?
"For instance, there's probably something invisible with lots of tentacles hovering behind your back right NOW."- Dear Old Barti, of course