All of which proves not a lot, except that it's extremely unwise to trust the police figures, which in statistical terms go in the discard pile. Let's expand the data set a bit - the Square isn't used solely for anti-war marches, and there have been two other large crowd events in the last couple of years that received wide coverage - the first is the 6/7/2005 2012 Olympics Award:
Seconds after London was proclaimed the Olympics winner the crowds that had packed into every inch of Trafalgar Square were sprayed with confetti.
The second is the Ashes celebration in September 2005.
The tens of thousands gathered in Trafalgar Square cheered highlights of the exhilarating summer series and interviews with each member of the victorious squad before a rendition of 'Jerusalem' rounded the presentation off.
[Note the photos, particularly of Michael Vaughan in front of a frankly enormous crowd]
and additionally
England's players joyously belt out the hymn Jerusalem one more time along with an estimated 100,000 well-wishers
while the Scotsman has
TRAFALGAR Square was transformed into a land fit for heroes yesterday as more than 30,000 gathered to toast the England cricket team's victory in the Ashes Tests.
Now, the Square is 110x110 metres, according to the GLA. That's 12100 square metres. Now, I reckon you can get four people in per square metre, which brings us up to a notional maximum capacity of, broadly, 50,000. 10,000 people would make the square look decidedly empty - if your commuter train came into the station 20% full you'd be well happy. From the photos I can see, the area is not 20% full, it's more like 80%, which would put 40,000 people in the square alone when Davide was taking his photos, not counting those still on the march.
So, what have we established? A large turnout for the Square itself is 30,000 to 50,000 people. More people were outside the square. I reckon we can conservatively estimate the turnout to be 50,000+, or sixteen times what the Met Police told the country's leading non-conservative Sunday broadsheets. Mind you, since their own website of forthcoming events doesn't mention the 24th February demo, perhaps they forgot.