The pair were leading the Melges 24 European Championships at Punta Ala, and the accident occurred when Merricks, Walker and crew, along with a second team sponsored by Glenfiddich, were travelling to a dinner in a 12-seater Land Rover.
Italian police are investigating what caused the loss of control, leading to the vehicle overturning. The 26-year old Merricks, from Scraptoft, Leicester, who lived in Titchfield, Hampshire, is thought to have died instantly.
Of the others, Sacha Nice, who also in the front seat, was treated for back injuries. Andy Yeoman is being kept in hospital for an ear injury, while Anna Hewitt was discharged after being treated for shock.
"I don't think I've ever met a nicer man in my whole life," Walker said. "He had incredible talent. There was not one ounce of malice in him."
"John was one of the outstanding sailors of his generation," the Royal Yachting Association racing manager, Rod Carr said. "He was an instinctive sailor with an uncanny ability to extract maximum speed in all situations. The partnership with Ian Walker made for a world-beating combination."Reuse content