Tamil protesters staging a demonstration in the City of London are now reported to be on the move.
It is understood that they are heading from Bank to the Commonwealth Secretariat offices at Marlborough House on Pall Mall.
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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.