Comment by tptacek

In case it's not clear from the story: a big part of the expense here is that the mural was painted onto the Royal Courts of Justice building, which is a Grade I preserved building, putting it in the same tier of building preservation as the Tower of London and the Palace of Westminster. Some of the things you'd do to get graffiti off a subway tunnel wall or a brutalist municipal building in the US (like using a high-powered pressure washer) can't be done to the RCJ building without risking damage to the structure.