Interestingly the BBC News Channel is showing aerial images of both Brexit marches in London - the anti-Brexit People's Vote March and the pro-Brexit UK Unity and Freedom March.
It's estimating the former to be attracting "tens of thousands" though not "hundreds of thousands" and the latter to be attracting around "a couple of thousand" people.
BBC reporter Jon Donnison is at the anti-Brexit march, and all the interviews so far have been with those attending that march.