The last two choices antedated the adoption by the Conservative party of leadership elections. Heath was the first elected Conservative leader.
(And Paul has a typo: 'Warpole' should of course be 'Walpole'.)
While Paul is otherwise generally correct, post-1066, Royal power in England only became absolute with William I. In Anglo-Saxon England the monarch(s) had to contend with the Witenagemot(s), which had considerable power including that of appointing and deposing the monarch.
The rise of Parliament was therefore seen and justified as the restoration of the ancient freedoms of the people.