Entire Roman streets and around 10,000 perfectly preserved artefacts have been uncovered in the heart of the city.
The discoveries have been preserved so well in muddy water that archaeologists have dubbed the site the 'Pompeii of the North'
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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.