First off, 'pure dead magic' is UK slang for really cool.
Pure Dead Magic is also a children's fantasy/science fiction novel by Debi Gliori. This is her first chapter book, although she has written and illustrated many picture books.
It is the story of a squabbling Scottish family dealing with a strange mish-mash of computers, magic, and the Mafia. As the story begins, the Strega-Borgia is facing a crisis, as the father has recently stormed out of the house in a fit of anger, and after an absence of three weeks has not yet returned. The mother is forced to take on a nanny, to help her with the children while she completes her degree in Advanced Witchcraft. Unbeknownst to her, the new nanny is also a witch -- and a much more advanced witch than is the mother herself. Other fun aspects of the story involve the family's pet rat, crocodile, yeti, griffin, and dragon, plus a good butler, a bad cook, and a gangster in a full bunny suit.
The basic plot revolves around the family getting their father, pet rats, younger sister, and bodies back. (It's that kind of story). The science fiction arises mostly from the fact that computers are used, and cyberspace is traveled through, although every bit of fiction involved seems to be primarily magical. The magic itself is a little disappointing, not being very mysterious, and not being very well planned out. The magical beasts, on the other hand, are quite spiffy.
The blurbs on the cover claim that the story is reminiscent of Harry Potter, Lemony Snicket, Mary Poppins, and The Addams Family. I assume that the Mary Poppins comparison comes solely from the fact that a no-nonsense nanny is involved. The Addams Family comparison is a little better, although the Strega-Borgia's are not morbid, just chaotic (although the general tone of the book is a bit morbid). Harry Potter is most likely mentioned because it's the biggest thing in Children's Fantasy, because both it and Pure Dead Magic are from the UK, and both have kids doing magic. Lemony Snicket; bad things, and gruesome things, happen in this book. Nothing that'll give you nightmares, but people get eaten, decapitated, kidnapped, and etcetera. It's more than you normally expect from a children's book. Personally, I'd throw Douglas Adams into the mix, because of its type of humour (although Debi Gliori doesn't lay it on nearly as thick as does Douglas Adams). This book is almost as much about the humour and playfulness as it is about the magic. I'd also compare it to Helen Cresswell's Bagthorpe Saga, for general familial chaos.
Overall, a good book. It isn't as tightly written as it should be, and at times the story line is a little hard to follow, but it was good enough that I'll read the next book in the series, when it comes out. (I think that if I were closer to the target age for this book, I probably would have enjoyed it more).
Speaking of the next book in the series, it's entitled Pure Dead Wicked, and will further the Strega-Borgia saga.
Update: The 3rd in the series is Pure Dead Trouble, the 4th Pure Dead Brilliant.