Birmingham had one that varied from about 2 to 150 people, depending on the weather. It was generally well-spirited and celebratory, without the aggro element you hear about in That London (which isn't to say there wasn't the occasional shouty motorist, but most people's reaction was positive). The only police entanglement I remember was when the Cathedral objected to people assembling on their grounds during choir practice (or something), and in the interests of diplomacy the meeting point was moved about a hundred metres to public land outside their fence.
Unfortunately, a core group of regulars decided to unilaterally change the day of month and start location, which didn't get publicised very widely because they did everything on Facebook. I've no idea if it's still going.
I hear good things about Leicester.