Boris Johnson today warned No 10 it must plough cash into London to secure Britain's recovery as he set out his vision to make it the "greatest city on earth".
The Mayor used his speech at City Hall this morning as a massive publicity plug for investment into transport.
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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.