last year, a dive by Oceangate’s Titan sub went tragically wrong. The vessel suffered a catastrophic failure as it neared the sea floor, killing all five people onboard.

On board were Oceangate’s CEO Stockton Rush, British explorer Hamish Harding, veteran French diver Paul Henri Nargeolet, the British-Pakistani businessman Shahzada Dawood and his 19-year-old son Suleman.

Rush said he had “grown tired of industry players who try to use a safety argument to stop innovation” and dismissed warnings that he would kill someone as “baseless”.

Most operators opt to have their deep-sea subs certified - but it is not mandatory.

Rush described his sub as “experimental” and, in a blog post in 2019, he argued that certification “slowed down innovation”.

The passengers on Titan paid up to $250,000 (£191,135) for a place.