Jade Jagger celebrated her 30th birthday on Saturday night by inviting 80 friends to a Hugh Hefner-inspired slumber party at the very proper Claridges of London. Eyebrows were raised at the typically subdued hotel when folks started to arrive in Playboy pajamas and underwear. Jagger, who wore a transparent vintage nightie, supplied her guests — including mother Bianca, former squeeze Dan MacMillan and current boyfriend Ben Elliott — with goody bags full of Playboy cigars, “A Night at the Playboy Mansion” CDs and Playboy videos and magazines.