Detectives investigating allegations linked to Jimmy Savile and others have arrested a 65-year-old man on suspicion of sexual offences, Scotland Yard said.
He was arrested at an address in south London and has been taken into police custody.
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Michael Fallon has received reassurances from his US counterpart that security ties with Britain will "endure" following a vote for Brexit.
On Friday, police said it appeared the girl had shot herself in the face with the weapon.
The showers will be slow-moving, heavy and thundery at times, particularly in central and eastern areas.