Art restorer Amy Griffin, from the Simon Gillespie Conservation Studio, says that it should be possible to remove the graffiti without damaging the original painting.
More top news
Labour leader tells May Day rally his party 'stand absolutely against racism in any form'.
Video has emerged of a police car colliding with a cyclist and driving over a bike during a mass bike ride in central London.
Harlesden's James DeGale has successfully defended his IBF super middleweight title against Rogelio Medina.