LONDON (Reuters) -Fire ripped through a superyacht in southwest England on Saturday, sending thick plumes of black smoke into the sky and eventually sinking the vessel after it briefly drifted across its marina. The Environment Agency said the yacht contained about 9 tonnes of diesel, prompting concerns about pollution and forcing local areas and nearby beaches to briefly close. Police and fire officials said the 85 foot (26 metre) yacht in Torquay, Devon, had been “well alight” by midday. The cause of the fire is being treated as unexplained. The police said no one had been injured in the fir…