A police spokeswoman said the boy's death was not being treated as suspicious but it was not clear if he fell into the water or went in deliberately before getting into difficulty.
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Hybrid Air Vehicles Ltd said a female member of staff was injured and taken to hospital as a precaution.
PC Stephen Hanson from Milton Keynes suffered severe burns when he helped passengers escape.
The Government is to launch a consultation on whether plastic packaging should be taxed in an effort to tackle waste.