A woman, who ITV believes was part of a musical quartet from London, threw eggs at the judges during last night's Britain's Got Talent live final. The channel confirmed 30-year-old Natalie Holt was a member of finalists Richard and Adam's backing group.
The London group Raven speculated that one of their members may have been involved in the incident.
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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.