"We found out about an hour later, having moved nearly half a mile in that time, that without a ticket we wouldn't get in."
Incorrect I'm afraid
Most people were paying on the gate. I certainly did on arrival at around 12:00
The "tickets only" sign on the roundabout on the motorway exit was misplaced - it seems it was intended for one specific car park.
Agree the traffic was horrendous - but it was made worse by poor lane discipline on the motorway, and people trying to break into the hard shoulder queue early, unsafely rather than going to the end and filtering in turn.
Using the hard shoulder as a ten mile slip road was just downright insanely dangerous