Alistair Frith is the British Home Secretary. He shut the Department of Domestic Defence down. It's responsibilities were handed to the special branch, because Alistair Frith thinks it is too expensive.
Through several Emails of Rook we know that Alistair lives in Oxford. He has a wife (Christine) and two daughters who are currently on vacation in Switzerland. Alistair has a pet schnauzer called Titania, which he loves very much. If Alistair isn't around the "beautiful" handler Sandrine Belllerose takes care of Titania. Alistair has an affair with Sandrine, he spents a lot of time with her and she stays over at Alistairs house. Furthermore he wants to make sure that she is safe. Alistairs wife Christine gets to know about the affair so she kidnaps Titania. Titania gets back savely, but after it Christine wants a divorce. Alistair also has an assistant called Giles Hopkins, who answers the unwanted emails, like those of Rook. In 2013 Giles gets fired and Kate Whitfield is now the assistant to Alistair.