The image of a hand grasping a knife can be representative of the increase in knife crime in Urban Britain. The red finish can symbolize a consequence of the knife crime; blood, which in itself is associated with death.
At a connotative level, the fact that the knife is white is almost a contradiction of itself; as white is usually associated with innocence and purity (e.g. wedding dresses, angels, etc).
The image of the wall covered in graffiti can symbolize Urban Britain's struggle - on a denotative level they're putting their controversial message on a wall, this may be a message to the government, who isn't listening - Like talking to a brick wall, literally.