Just a rock is a poster that debates the idea of "Britishness" and questions an individual’s perception of what British means to him.
The dialogue is from a radio show in which George Galloway dismisses a listener’s view of being more British because he is white. The message here is to show that we are only a nationality by chance; we have no choice of where we are born. Borders shouldn't dictate our values or beliefs and the land we stand on is just rock.