The Duchess of Cambridge handed out sprigs of fresh shamrock to members of the 1st Battalion Irish Guards, as part of a St Patrick's Day tradition.
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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.