Actually I suspect the time frame is much shorter than a year given all the plans and organisation that such events require and the various financial commitments that have to be made. I would put it at 6 months myself.
And for the record I am not seeking to get the event 'banned' just moved to a more sensible location, as I simply do not think that tinkering around the edges with marshals will be sufficient if the majority of people are still going to drive and need to park in spaces which do not exist. I see nothing wrong with Crystal Palace- it seems a very suitable venue and I know similar events have been held there before. And its fairly easy to get there from Forest Hill.
What also seems to be missed in the discussion is that such heavily attended events are not that inclusive as most people with young children will not want to take them there as its difficult for them to run around safely without being trampled on. This was our experience last year and the reason for leaving early, and our main reason for not planning to go again this year. It is not fun for young kids or their parents , but I suppose even these groups will be accused of threatening the economic future of FH by their inflexibility and lack of tolerance.