We aren't talking about a painting in a private gallery, it's a big object in the middle of the street. If it was actually unauthorized it would be removed, even if the British government respected free speech. If artists could actually place at night their works and not be removed, the streets would be blocked due to the number of statues. This clearly seems to be a sponsored work with typical Banksy marketing, like the work that got half-shredded at its auction.