Banksy is a anonymous street artist, being anonymous means they would be unable to claim any copyright over their work without revealing their identity. Banksy also famously stated “copyright is for losers” in his own signed graffiti. NHS hospital corridors being classed as a public place and not a private gallery further protects our ability to re-create this work using high resolution photos taken by ourselves.

Banksy who once claimed "copyright is for losers" sued an Italian museum  for copyright infringement | Adland