I think Cameron would be a conservative were he American. But a disillusioned, troubled Republican. Does he even pretend to have anything much in common with the Party of Newt and Palin? No, not really. Neither they nor Romney have been invited to speak to the Tory party conference and nor will they be. No, the Republicans Cameron invites to speak to the Tories are Schwarzenegger and John McCain. Even then it's the 2000 vintage of McCain the Tories have in mind, not his current incarnation.
(Admittedly, there are a good number of grass-roots Tories and a good deal of the conservative commentariat that would like Dave to be more like the GOP. On the other hand, he'd quite like to win the election.)