Not quite the same, but a few years ago we were going to Heathrow, we were slow getting on to the motorway from the slip road but we got on. Turned out that there had just been a huge police raid, guys on the ground with guns to their heads etc., etc., we had a quick shufty as you do and drove on.
Ten minutes later, they closed the slip road and stopped all traffic for forensics, it was closed for 4 hours. We would have missed our flight and by default our holiday in Ireland.
Again, just that scenario of another minute either way.....