In recent years, graffiti art has become a big business.
The UK government estimates that the value of the street art trade has grown by £15bn to £65bn.
The number of graffiti art works in the UK has also increased by nearly 60% in the past decade.
A recent study by the UK-based artist collective Mouldy Lads estimates that a graffiti mural will cost between £20,000 and £25,000.
The average cost of a work is about £500.
But many artists, including some of the best known, have faced the prospect of arrest or even deportation from the UK, even for a minor offence.
What is graffiti?
There are three main forms of graffiti graffiti, but the main differences between them are: colours: this is the most common form of graffiti, usually a series of coloured dots and letters