I watched the London Marathon not far from Buckingham Palace with a friend. We had free tickets.
I saw an incident near Buckingham Palace at the end of Pall Mall when I saw two males run across the road where the leading runners were and it looked as if some people were trying to knock a runner off course. It was all very sudden and chaotic, and spectators looked round and wondered if it was going to be another terrorist attack.
Some event staff tried to grab them and that was all I saw and people went back to normal. It was quite weird.