Just arrived back from Shoreham (relatively local to us). From a high vantage point we could see the A27 has stationary traffic for several miles east of the incident, and being familiar with the airport it's going to be a long, long job getting the spectators off the premises (the traffic lights at the north entrance being where the incident is). Fortunately we were on a motorbike, and were able to leave the area quickly (just as several roads were being closed to all but emergency vehicles).
By a stroke of luck we decided at the last momennt to spectate from the hill opposite (best place to watch XH558 from anyway); if we'd gone to the show we'd have been queuing at exactly the wrong place and time.