There weren't many demonstrators at all, really. Most of the noise was coming from a group of people asking for someone imprisoned in Turkey to be released. There were many EU flags, but few people holding them; they were attached to railings and so on, along with some placards that probably sounded better at the committee meeting that decided on the wording.
There were also people dotted around the square with these.
They were getting honked at, too, maybe 3 or 4 times a minute (not counting ones that honked twice). The people honking them were driving trucks, taxis and (on at least one occasiona) a London bus. Only rarely were they honked by car drivers.
OK, given the amount of traffic present in the square, once every 15 or 20 seconds isn't a lot. London is the most pro-EU part of England, though. All the London newspapers are pro-EU. All the commercial radio stations are pro-EU. All the flags around the square were pro-EU. Still, though, there are not small numbers of Londoners honking their horns at anti-EU signs.
Those people asking for a "people's vote" to break the Westminster deadlock are, on the whole, of the opinion that the people will vote their way this time round. They may be in for a (second) shock.
If a referendum got us into this mess, I can't see one getting us out of it.
The next referendum I want to see is the one that proposes the UK should have no more referenda in future. They're almost invariably a bad idea.