LOL - research commissioned by the same government that rammed the thing.
http://www.bbc.com/news/uk-23370270
Note:
But sports economist Stefan Szymanski said it was impossible to tell how much of the economic activity could be put down to the Games.
"It's almost like a bit of creative accounting. There's no way of testing whether what they're saying is really true."
Jonathan Portes, director of the National Institute of Economic and Social Research and a former chief economist at the Cabinet Office, said attributing the economic benefits to the Olympics was "a little far-fetched to say the least".
To make even a rough guess of the extra business generated, you need to have a sense of what would have happened anyway; what academics would call "the counterfactual".
They never really provide that in today's glossy report. The implicit assumption seems to be that - had it not been for the Olympics - that £9bn would simply not have been spent.