Did Cameron arrange the Cable Sting?

This is the dynamite question, the one that has the potential to bring down this government. Whose idea was it for The Telegraph to conduct a covert recording on Vince Cable in December 2012? Could it have been the Tory leadership? If this was demonstrated to be the case, then the Tories have deliberately destroyed the reputation of a Liberal Democrat colleague, and the coalition would immediately come to an end.