This article caught my eye in today’s Independent Online:

When Banksy offered one of his highly sought-after canvases to Labour to auction for Ken Livingstone’s ill-fated re-election campaign, the party’s high command was jubilant.

They were left with a conundrum, however, when they realised that the secret identity of the famously elusive graffiti artist would cost their hard-pressed coffers tens of thousands of pounds.

The winning bid for Sketch for Essex Road, a canvas of two children with hands on hearts pledging allegiance to a Tesco carrier bag on a flagpole, was £195,000. But that meant Banksy’s painting would have to be declared as a gift to the party, requiring it to release his true identity on the internet along with hundreds of other donors – blowing apart his well-guarded anonymity.
He’s anonymous, so Banksy’s gift is impermissible – News, Art & Architecture – The Independent