You could of course, believe the government on this.

From todays Independent:

Originally, the Royal Parks Agency banned the rally in central London on 15 February, arguing that the soil would be too wet to cope with so many people and that there would be a safety risk as protesters left in the dark.

But Tessa Jowell, the Secretary of State for Culture Media and Sport, said yesterday that she had given the go-ahead for the protest after failing to find a better venue. Extra lighting will be installed, and marchers' arrival and departure times will be staggered.

Ms Jowell said: "The right ... to organise and take part in peaceful marches and rallies has never been questioned. The issue has only ever been to find a venue that is as safe as possible."

And that seems reasonable enough to me.

Ed