Nick Milligan, 51, and his eight-year-old daughter Emily died after they were thrown from the family’s boat and then hit by the vessel. His wife and three other children were injured.
The vessel was finally brought under control by a waterskiing instructor, who jumped on board as it circled off the coast – an action that police said prevented further loss of life.
Detective Superintendent Jim Colwell said Mr Milligan’s wife, Victoria, 39, and their four-year-old son, Kit, remained in hospital with “serious, potentially life-changing injuries”, while their two other daughters, Amber, 12, and Olivia, ten, suffered minor injuries in the accident, near Padstow in Cornwall.
The BSkyB media executive, who has family links to Scotland, lived in south London and owned a holiday home at Daymer Bay, close to where the accident happened.
The family had been enjoying the bank holiday weekend in the popular harbour area when the accident happened, shortly before 4pm on Sunday.
A joint investigation is being carried out by police and the coastguard.
Mr Milligan’s brother, Max – a photographer who describes himself as a Scots native in his recent book The Soul of Scotland – said: “Nick, or Nico as he was known to us, was an extremely loving father and husband.
“As children and teenagers we spent many summers and New Year’s Eves at New Polzeath here in Cornwall and a few years ago he built his dream home above Daymer Bay.”
He went on: “That he and my delightful niece died at their favourite place at the end of a gloriously sunny bank holiday weekend provides us with a tiny glimmer of light.”
Colleagues paid tribute to Mr Milligan, the managing director of Sky’s advertising sales division, Sky Media. “Everyone at Sky is deeply shocked and saddened to learn of the tragic accident involving the Milligan family,” a spokesman for Sky said.
“Nick has been a great friend and colleague for many years and his loss will be felt across our company and the industry. Our very deepest sympathies are with his family at this time.”
Ben Fenton tweeted: “Nick Milligan …was one of the kindest, nicest funniest men I have ever met.”
Eyewitnesses said the boat had been seen to veer to the right, throwing the family overboard. It continued to circle in the water until waterskiing instructor Charlie Toogood leapt into the speedboat to turn off its engine. A second man, Will Jones, was also said to have gone to the rescue.
Matt Pavitt, of the North Cornwall Coastguard, said: “Thanks to some incredible seamanship and bravery from some locals, they managed to get the boat under control and stop it from causing any further damage or harm.
“This boat is eight metres long with a very, very powerful engine on the back.
“It is going round and round in circles and one of the local boatmen, we understand, was able to get alongside it and somebody actually jumped from one boat to the other to bring the boat under control. So, incredible bravery which undoubtedly saved lives.”
He added: “Reports are that the boat was seen to veer over to one side, causing all six people to end up in the water and then the boat is known to have circled a number of times, hitting some of the people in the water.”
Alex Greig, of Falmouth Coastguard, said safety features in vessels such as the one driven by Mr Milligan, usually included a so-called “kill cord”.
He said: “If somebody is thrown away from the console, it should disable the engine.
“But if it’s not working, or not being worn correctly, there is the chance that if you are thrown away from the boat, it will continue to move under its own power.”
Mr Milligan and his wife had been married since 23 October, 1999, according to his Facebook page, and they both studied at the University of Reading.