Johnson campaigned as being a conservative, but when he governed, he was governing from the left.
He's just an arrogant, entitled opportunist, with no deep-seated ideological views either way. It's notable that when he ran London as mayor, he took great pains to position himself as a lot more liberal and cosmopolitan than the traditional Tory... purely because that's what the voters wanted.
"Well, look, I'm - I'm very pro-choice,"
-Trump 1999
“In many cases, I probably identify more as Democrat”
-Trump 2004
“Hillary’s always surrounded herself with very good people. I think Hillary would do a good job,”
-Trump 2007