Hugh and I had a very good meeting with the London Marathon Team- they have been contracted by the London Olympic Games Organizing Committee to provide the logistics for the marathon and race walks.
This included placement of crowd control fencing and the exact road usage for the runners.
Tuesday - June 12 (today)
It finally stopped raining around 10 am. I think here in London when they have a drought, they still report a 75% chance of rain!

Hugh and I biked the course to review the turns.
There is still some fencing and contruction materials around the monument in front of Buckinham Palace that might prevent us from measuring the race walk course. If that's the case, Hugh will do all the preliminary work and I will do a measurement that day.
We plan on layout and measuring a calibration course on the Mall (straight road way where the races start and finish). We are confident that this cal course will not have any obstructions during the Olympics. It should be ideal if we need to do any additional measurements.
One personal note:
You haven't lived until you have tried to follow Hugh on his bike throught the traffic of London. I have bike the path from his house to the Mall (start/finish) several times and will consider the Olympic measurement a success if I don't get killed before I have a chance to measure it!