The excavation will descend over 50 feet below the surface say reports, deeper than the height of nearby houses, and will feature a 45-foot swimming pool, hot tub, sauna, massage room, ballroom, covered courtyards, staff accommodation, parking, a turning circle and car lift.
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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.