If the council does not own the building then I'm unsure what rights they have to remove it, but no doubt they will find some regulation somwhere. And if so, should the building owners not be responsible for doing this rather than London tax payers which I am thankfully not one.
That said I actually find this one quite amusing and unoffensive and I'm no great grafitti lover. Perhaps the painter they use to paint over the mural will find his "work" offends someone else who might then demand that this be painted over again. Silly thought I know.