- Emergency services say there are "multiple casualties"
- The M11 is closed northbound from junction 7 to junction 8
- The crash involved three cars, a lorry and a horsebox
- Five fire crews have been sent to the scene
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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.