A spokesperson for Crossrail has told ITV London that the worker who has died was spraying concrete when a piece of concrete from the ceiling fell and hit him.
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Paramedics were on standby outside the police cordon as armed officers stood by the property.
A team of researchers has taken samples from the ten busiest London Underground lines to work out which are the dirtiest.
The action comes on top of an emergency timetable which has seen hundreds of trains a day being axed.