I think Cameron, Johnson and Blair are quite different psychologically.
Johnson strikes me as a psychopath. He’s definitely got no inner moral compass.
Blair I think is someone who sort of drank his own kool-aid. Because a lot of his decisions were good and because of the fatal left-wing flaw of believing you occupy the moral high ground, combined with his religious leanings, he developed a sort of Messiah complex. I don’t think he is actually ‘bad’ person.
David Cameron seems like a typical slightly dim, arrogant posho, surrounded by people like him, who succeeded beyond his abilities and ran away when things got difficult. I don’t think he feels shame (maybe embarrassment), I certainly don’t like or respect him, but he has good qualities as well as bad - eg he seems to be a loving husband and father (as does Blair).