American magician Milbourne Christopher investigated, failed to observe anything that could be called paranormal, and was dismayed by what he felt was suspicious activity on the part of Janet. Christopher would later conclude that "the poltergeist was nothing more than the antics of a little girl who wanted to cause trouble and who was very, very, clever."[
Skeptic Joe Nickell has criticized paranormal investigators for being overly credulous: when a supposedly disembodied demonic voice was heard, Playfair noted that, “as always Janet’s lips hardly seemed to be moving.” Nickell wrote that a tape recorder malfunction that Grosse attributed to supernatural activity and psychologist and president of the Society for Psychical Research David Fontana described as an occurrence "which appeared to defy the laws of mechanics" was merely a peculiar threading jam common to older model reel to reel tape recorders. Nickell noted that the supposed poltergeist "tended to act only when it was not being watched" and concluded that the incidents were best explained as children’s pranks. According to Nickell:
"Time and again in other 'poltergeist' outbreaks, witnesses have reported an object leaping from its resting place supposedly on its own, when it is likely that the perpetrator had secretly obtained the object sometime earlier and waited for an opportunity to fling it, even from outside the room—thus supposedly proving he or she was innocent."
Nickell states that a remote-controlled still camera (the photographer was not present in the room with the girls) timed to take a picture every 15 seconds that supposedly “recorded poltergeist activity on moving film for the first time” was shown by investigator Melvin Harris to reveal the girl's pranks. A photo allegedly depicting Janet "levitating" in mid air actually shows her bouncing on the bed as if it were a trampoline. Harris called the photos examples of common “gymnastics,” and said “It’s worth remembering that Janet was a school sports champion!” Nickell also wrote that demonologist Ed Warren was "notorious for exaggerating and even making up incidents in such cases, often transforming a "haunting” case into one of “demonic possession.”
In an interview with the Daily Mail, the adult Janet admitted that she and her sister had faked "2 percent" of the phenomena, prompting Nickell to comment, "the evidence suggests that this figure is closer to 100 percent." 
http://en.wikipedia.org/wiki/Enfield_Poltergeist