Virgin founder Sir Richard Branson at a press conference in Mojave, California, after the crash of his prototype spacecraft in October. Photo: AFP

London: Sir Richard Branson has quietly shelved an ambitious plan to pilot a submarine to the deepest points of the world's five oceans.

The entrepreneur had a grand scheme to explore both space and sea. But his plan for the first rocket ship charging passengers for trips to the edge of space is in jeopardy after the craft crashed during a test flight, killing a pilot.

Virgin Oceanic's DeepFlight Challenger submarine was unveiled in a blaze of publicity in April 2011, with Sir Richard describing its mission as "the last great challenge for humans".

He had hoped the six-metre-long submarine, designed to "fly" along the ocean floor, would make its maiden voyage to the bottom of the Pacific's Mariana Trench - at a depth of 36,000 feet, the lowest known point on Earth - by the end of 2011, or failing that, by 2012.

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It would then move on to the Puerto Rico trench at 28,000 feet in the Atlantic, followed by dives in the Arctic, Indian and Southern oceans. The plan was for alternating pilots in the single-seater craft, with Chris Welsh, a sailor and explorer, taking the first dive and Sir Richard the second.

Three years on, the DeepFlight Challenger has been mothballed, never having reached the bottom of any of the oceans. The Virgin Oceanic website - which had promised "five dives, five oceans, two years, one epic adventure" - no longer exists, apparently taken down earlier this year.

Virgin Oceanic had planned to charge a future generation of "aquanauts" up to $US500,000, according to one source, to pilot submarines to the ocean floor.

But the company that built DeepFlight Challenger has refused to back the project, insisting the submarine was suitable for only one dive and could not be reused because of the pressure on its structure at such depths.

In a little-noticed statement three months ago on the Virgin group website, Sir Richard alluded to the project being scrapped but stopped short of admitting defeat. He said: "Starting new ventures takes a 'screw it, let's do it' attitude and finding the right partners to help us achieve the unthinkable . . .  However, business is also about knowing when to change tack.

"We are still highly passionate about exploring the bottom of the ocean. However, we are now widening the focus of the project and looking for new technology to help us explore the ocean and democratise access at reduced cost and increased safety."

Last week, Virgin confirmed the original plan for five ocean dives using DeepFlight Challenger had been scrapped. A spokesman said there were concerns about making the dives safely, adding: "We were not sure it [DeepFlight Challenger] would make it down. That project has been put on ice while we look at other technology that works."

DeepFlight was beaten to the record dive by another submarine, piloted by James Cameron, the Oscar-winning film director, who took his submersible on a solo voyage to the bottom of the Mariana Trench in 2012.

Telegraph, London