"Cameron has ben succeeding very nicely with more pragmatic and humane brand of toryism - and presumably - Davis is really pissed off about it - and so he has selected this little mound on which to stand and organise resistance."

This is possible and at least it seems to make more sense than some of the other theories I have heard.

However, I don't actually believe that Cameron really is to the left of Davis, I think he is just trying to get elected by any means possible, pandering to anyone if he thinks there are a few votes in it. I can't understand why people can't see Cameron for what he is, a slick snake oil salesman. Tear the mask from Cameron and you reveal the hideous features of none other than the evil old crone, Thatcher. Although Blair told lots of real lies in his time as PM, he was telling the truth when he said he admired Thatcher and wanted to continue with conservative policies. In effect Blair was a Tory but ironically people didn't believe him, at least at first. This is not the case with Cameron who I think is lying through his teeth when he talks about humane Toryism.

As to why Davis is doing this I am not sure but it's obvious that they don't like each other all that much and Davis will still be very resentful of Cameron's leadership win. I suspect that they might have had some kind of bust up and Cameron told Davis that he wont be in the Cabinet if the Tories win the next election, or at least Davis might have got an inkling that these were Cameron's plans. So what does Davis do? He will have seen what happened to Hesseltine when he walked out of the cabinet, he never became leader. So he pretends to have concern for civil liberties, so much so that he resigns his seat to conduct a farcical bi-election. He then comes back on the backbenches hoping for Cameron's fortunes to take a nose dive when he can make his own bid for the leadership. Of course, Davis's chances are still pretty close to zero but he his too arrogant and vain to realize it.

Well it's as good a theory as anyone's.