Well we've had similar riots here in Denmark several times, where left wing extremists run rampant destroying everything.
Luckily our police-force has dealt with this kind of thing many times by now, and know how to deal with it.
A wall of amored vehicles split the protesters, you don't move you get run over... After that several walls of amored policemen with shields, mace and clubs and teargas grenades - simple but effective.
We've also got a few amored trucks with waterguns, if the water itself doesn't make a difference you can mix mace into the water and get people moving that way.
Policemen in civil clothes normally go into the demonstration and report back on what's going on and where they are moving.
I believe that people have a right to protest and riot, as long as they are ready to face the consequences, which should be hard and swift.
Sounds like you guys need the army to go in and bring some order to the proceedings over there :/ I really feel for the people living/working in the areas affected.
Weird to think that I was staying in East Croydon less than two weeks ago, guess I was lucky :/