OK, so he admits that nothing actually happened as a result but:
While there are always arguments over the size of demonstrations (the 2 million-or-so figure we claim is supported by considerable polling and photographic evidence), there is no dispute that this was not merely the country\’s biggest political protest, but the biggest by a substantial order of magnitude.
Just what is a "substantial order of magnitude"?
One order of magnitude is times 10 (or divide by ten). I agree that there\’s not been a 20 million strong demonstration: but I\’m absolutely certain that there have been 200,000 strong demonstrations (at least one of the Countryside Marches was that large). So it\’s not the largest by one order of magnitude, let alone a "substantial" one.
So what is he talking about?