The March of the Beekeepers through Parliament Square comes ahead of a major vote in Brussels on Monday. Environment Secretary Owen Paterson is expected to vote against a ban on some neonicotinoid pesticides, which campaigners say are contributing to a decline in bee populations.
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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.