An emergency worker had to be freed from his car after a tree fell on it.
It is believed the severe weather contributed to the tree fall in Hive Road, Bushey, at around 5.30pm yesterday.
Police closed the road at the junction Common Road, in Stanmore, Harrow, for several hours while emergency services freed the man from his car.
He was taken to a major trauma centre by air ambulance.
Traffic was gridlocked in all directions for more than one hour.
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