The Sun (and the Daily Mail , for that matter) have been strangely coy about this story following their earlier excitement over it (see here, here, here, here, here, and here). I heard this on the radio a couple of days ago, and this is the story as reported in The Register.
…turbine manufacturer Enercon's interim report says bolts holding the blade to the hub failed, and it's now "carrying out further tests to establish what caused the bolts to come loose, focusing on the blade and hub components to which they were attached". Dale Vince, co-founder of site operator Ecotricity, elaborated: "The bolt failure was the effect not the cause of the problem. They have ruled out bolt fatigue and design problems, and we know that they were properly put on."
The full/original story can be found in The Telegraph. Interestingly, The Sun still isn't giving up. Its own version of the story says:
A WIND turbine destroyed as stunned eye-witnesses described seeing strange lights in the sky did NOT have a close encounter with a UFO, scientists insisted today.
It goes on to repeat all that guff about UFO hunters flocking to the site, and persists in saying the blade was sheared off instead of just saying it sheared off – implying something did it. The funniest thing about this is that The Sun was prepared to do its own highly (un)scientific investigation, but it won't accept a proper one by proper scientists. And Nick Pope was unavailable for comment. He believes himself to be on a diplomatic mission to Omicron Persei 8.