Given that the British state is still keeping secrets from the First World War, it is obvious that we will not learn much from that source until perhaps the year 2111, and it will be left to the realm of speculation and theory as to what motivated the mandarins to overthrow Gaddafi's regime. However, my own belief is that Gaddafi's pursuit of the gold Dinar was where he crossed the line and became a threat to the shadowy powers that be. This was not, of course, a military threat. The idea that Libya posed any kind of military threat was always ridiculous, and clearly indicated by the ease with which NATO blitzed the country. No, the gold Dinar was a dagger pointed at the heart of the rotten world monetary system.
The clip below discusses this plan of Gaddafi, although I have a few quibbles with some of what it says (such as "a country's wealth would depend on how much gold they have": not so!), it certainly indicates the clear and present danger Gaddafi signified to our overlords.