Police have made another appeal for witnesses to come forward after a teenager was shot dead on a residential street in Battersea.
Police believe "a number of young people" may have information about the course of events that led to the death of 19-year-old Kyle McDonald.
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The plaque at number 16 Cowley Street in Westminster marks the brown brick Georgian townhouse where Sir John lived for 31 years.
A man reportedly armed with several knives has been arrested in Whitehall on suspicion of planning a terror attack, police have said.
Metropolitan Police officer, Tom Harrison, has been crawling the course since the race began on Sunday morning.