One consequence of sharing some stations with other train operating companies is that we get the fallout when their standards slip even lower than ours.
So spare a thought for station staff at Moorgate, Old Street and Highbury & Islington. Great Northern have omitted to clean their tunnels properly for a couple of decades, and the dust has now become a positive nuisance. The good news is that it doesn't - as initially feared - contain asbestos. The less good news is that it contains mould and various other nasty substances.