Cameron has been a weak leader, which is the very reason we are getting a referendum.
Ever since Heath took us into Europe, without a public vote, the Conservative Party has been divided, and almost impossible to lead. Thatcher did it with a huge majority, and Major kept the Party together by sheer hardwork. Then Hague, IDS and Howerd tried to lead a broken Party and failed.
Even after 13 years of Blair/Brown tyranny, the public still could not vote for a Conservative majority, so Cameton led a Government with his hand tied behind his back.
Cameron's early call of a referendum had to be seen as a brave move. Win (with a stay result), then he can he can properly rule and lead a united party (there may have to be some sackings). Lose, and he will have to fight a leadership election and probably lose (watch for Boris' manoeuvring ).
Either way, after the referendum, the leading of the Conservative Party will be clearer and easier for the eventual winner.