I went to WZD in Bristol last year. There were around 1500 zombies chasing brains as we walked from one end of town through Bristol city centre to the other, in amongst tourists and shoppers going about their daily business - oh the look on their faces! As you can see from the video, some people went all out on their costumes, and it basically made for a great event so I would hope we would all make a good effort too.
The whole event lasted about two hours roughly, with us all meeting in a park, doing the zombie walk (like a proper zombie with arms out and groans for braiiiins), which itself lasted about 30 minutes. So I would expect something similar for London.
I'll keep you all posted about this as we get closer, but it'd be worth getting it in your diaries, and getting all your gear ready for a really good day of feasting on braiiiins.....
"World Zombie Day is an international annual event that grew from Pittsburgh’s first Zombie Walk at Monroeville Mall in 2006 – the site where George Romero filmed Dawn of the Dead - to help all fans of Zombie culture come together in an international effort to relieve hunger and homelessness. More than 50 cities worldwide participate in World Zombie Day, including New York, Pittsburgh, Paris, Hong Kong, Los Angeles, Chicago, Dallas, Seattle, and Tokyo."