Starbucks wrecked after Gaza demo in London

Demonstrators smashed the window of Starbucks in High Street Kensington after the rally for Gaza earlier today. Here's the Beeb report:

Thousands of demonstrators have marched through London to call for an immediate ceasefire in the conflict in Gaza.

The protest started peacefully but there were confrontations as police tried to move demonstrators away from the gates of the Israeli embassy.

The windows of a Starbucks was smashed and three police officers were injured as a minority of people threw missiles.

The Metropolitan Police says 20,000 people marched but the BBC estimates the figure could be as high as 50,000.

Now the police were in a far better position to count I would have thought so how did they get so low a figure? Also, are the BBC saying that the police are lying?

The BBC actually filmed the Starbucks window smashing so here's that link again.