As far as I know easyJet do overbook their flights.
It's a definite change in policy, if so. Back in 2000 the business model was no overbooking, so they said, and no SBY policy. There was no way to issue a SBY ticket. They knew, back then, that many people on the main commuter routes e.g. STN-GLA/EDI booked very early and bought 2 tickets and an early & late flight. On Friday nights they had many no shows, but they had sold the seats. I wonder if this started the thinking of overbooking; but I was told the computer booking program, then, did not allow overbooking.
To add to this discussion, and considering the UAL and recent ez scenarios, I was told some years ago, before the meteoric rise of the LoCO's, that the regular airlines overbooked by 5%-ish. Indeed they were allowed to do so by the authorities. True, yes/no? there will be those who know.