Sir Peter Hendy, the head of Transport for London, said that the success of the Olympics showed that it was possible to take some space away from traffic without causing gridlock.
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The 24-year-old was unarmed and the incident is not being treated as terror-related.
Some platforms have been taken out of service with disruption expected to continue until the end of the day.
The Met Office has extended its weather warnings for snow and ice to cover vast swathes of the country, including London and the South East.