The Shadow Secretary of State for Transport, Maria Eagle, says the Heathrow spur of the high speed rail network would cut down on domestic flights and improve the overall capacity of the airport.
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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.