Metropolitan Police Commissioner Sir Bernard Hogan-Howe said that he was "shocked" by allegations that undercover officers hunted for information to smear the family of murdered teenager Stephen Lawrence.
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Man who has barricaded himself in house for three days may have a stash of petrol and other explosives, police say.
Transport secretary Chris Grayling said MPs will decide this week about where to allow airport expansion in south east England
The Met Police has thanked residents in Northolt for their patience but has warned the armed stand-off could take time to resolve.