This report emerged yesterday:
Wrong air passenger bypasses Gatwick security | The Post
Interestingly, through Facebook, a heard from a friend who had been on the very same flight. He reported that it was only at the repeated head counts did anyone notice there was something amiss. Identifying the passenger's checked luggage involved some walking down the aisle holding bags up for passengers to identify...
OK, so maybe a couple of gate agents checked the name and flight number / destination, but missed the date, while boarding a hundred or so people. But how did the pre-security scanner not pick this one up?