Alan Andrews from ClientEarth gives his reaction to today's Supreme Court ruling that the Government is breaking it's legal obligations to protect us from air pollution.
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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.