Wiggleigh
Mr Wiggleigh is a bledlow at Unseen University. He is trusted enough by Mustrum Ridcully for him to have acted as a go-between on the night when Samuel Vimes did not need magical help from the wizards, did not go within a quarter of a mile of the university, most emphatically did not discreetly climb over the back wall to get in, and did not speak to Ridcully in Mr Modo's gardening hut whilst suffering inconvenient onions. Wiggleigh would be happy to vouch for this.