Come on opening an unlocked door is not breaking in.
"Breaking" doesn't actually require that anything be "broken" in terms of physical damage. Someone who has permission to enter part of a house, but not another part, commits a breaking and entering when they use any means to enter a room where they are not permitted.
Scenario: Capita's Uninvited eNforcement Team enters your home to see if you have a TV, is that illegal entry if you left your door open?