The cousin of a billionaire who lost his life on the Titan submersible last week said the last time she saw him was during a visit to Booker Airfield in High Wycombe.

British billionaire Hamish Harding was one of five people to die after the Titan submersible imploded during its descent to visit the wreckage of the Titanic at the bottom of the North Atlantic Ocean last week. 

Kathleen Cosnett from Twyford, near Woodley in Berkshire, told the media last week that she didn't think the rescue effort to save her cousin had been quick enough, adding that she believed communication between the submersible and its support ship was "handled badly".

"The hours that were lost before the alarm was raised were at a great, great cost. Now we know that it likely imploded on the descent, it really is the best outcome. They wouldn't have known it was coming."

Kathleen also remembered the last time she had seen Hamish, back in 2002 when he took her on a private aeroplane trip from Booker Airfield in High Wycombe.

"Adventure was really important to him. He did die doing what he loved. That's what his family have said too, and we all agree."

Speaking to the Daily Telegraph last week, Kathleen described her cousin as "daring" and "inquisitive", adding that she had been "devastated" to learn he was missing.

The Titan submersible lost contact with its support ship after submerging off the coast of Newfoundland in Canada on Sunday, June 18.

A frantic four-day rescue effort followed, before a remotely operated vehicle discovered debris from the submersible on the ocean floor near the Titanic wreckage.

The US Coast Guard announced on June 22 that Hamish Harding, alongside UK-Pakistani businessman Shahzada Dawood, his 19-year-old son Suleman Dawood, American pilot Stockwood Rush and French national Paul-Henri Nargeolet had been killed instantly in what authorities described as a "catastrophic implosion or sudden collapse inward" of the vessel. 

Efforts to recover the bodies of those who lost their lives are ongoing, though the coast guard has warned that they may never be found.