Yay! We'll be there! It was great last year.
I have no inside info on MN but I know the school and the event so can take an educated guess.
Queensbridge Infants had the genius idea, last year, of holding a community yard sale (they called it the London Fields Jumble Trail). It works like this:
They have a fairly large zone around the school and you have to pay £10 to be included on the map, which gets printed and shown on the web. (You give an idea of what you'll be selling). Anyone who lives in the area can do a sale, you don't need to have DC at the school.
At the end of the day, you donate as much of your profit as you like to the school - could be everything, nothing or any amount you like. (We gave everything except we let the DC keep the little bit of money they made selling toys).
Local businesses can go on the map too but they have to pay more.
The absolutely genius bit of it is the PTA never has to handle the money - it's all done online through a crowdfunder. And, they did really well.
It was good fun last year. Some of the roads near the school had a huge number of houses taking part so there was a great atmosphere. (We're a bit further out).
I understand there was stuff on for the DC in a square near the school too but we didn't make it that far.
I've been trying to persuade my DC's two schools to do this ever since, It's such a genius idea IMO. (We live outside London, but have family there. I was up there last week helping turn out cupboards and find old toys & bric a brac in decent condition to sell. Some of the toys were from the 70s and before!).
How did MN get involved? After the success of last year, I guess perhaps the PTA or teaching staff approached them for sponsorship and MN said yes?