Prince's Sporting Club in Surrey has pleaded guilty at Southwark Crown Court to corporate manslaughter after 11-year-old Mari-Simon Cronje died when she was hit by a boat towing the inflatable she was riding.
Company director Frederick Glen Walker was cleared of any offences after the Crown Prosecution Service dropped charges against him.
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Mr Charles died in hospital after he was chased by a police officer into a shop in Dalston and restrained.
The Labour mayor will seek a second term in City Hall.
The Apprentice boss tweeted a picture of the sports team, which had been edited to include a picture of handbags and sunglasses.