Shootings in suburbs happen regularly.
In terms of violence between the homegrown firms...they happen and it gets just as messy as stuff in other countries.
George Bromley from Liverpool for instance used to tax rival drug lords. His favourite method was kidnapping a rival and putting a red hot iron to the guy's scrotum. Also in Liverpool rivals shoot each other to pieces regularly. The same things happen in Manchester.
In London there was a crime firm from the East End which moved into the drug's business by violently hijacking other drug lords and dealers. This included kidnapping the guy and taking him away to a cellar after which they smashed the guy to pieces with a sledgehammer. Read the book Judas Pig by Horace Silver if you want to know more about this firm. It's a novel but it's based of situations that really did happen. The same firm also once tortured a guy in a slaughterhouse for two weeks, cutting him to pieces slowly, after which they burned him while he was still, but barely alive.
Notoriously gruesome things happen in Great Britain. Just as bad as the things that happen in the USA or Italy.