The points in the slide were "supported entirely" by investigations conducted so far, the spokesperson said. Other potentially risky decisions taken on the rig included Halliburton not re-evaluating the cement slurry mix or waiting for foam stability results, as well as BP not running diagnostics on the well, not using a cement log and not installing additional plugs to the well.

Meanwhile, investigations have still not uncovered what happened to the blowout preventer, which sits on the well head and is intended to prevent this type of accident. Forensic examinations on the device are continuing.

In a document presented to the OSC this week, experts said blowout preventers must in the future be equipped with "diagnostic tools", similar to black boxes in aircraft. These would be used to "provide more information in the case of a blowout".

The document also concluded that better information sharing and oil spill tracking technology should have been in place at the time, and was developed frantically in response to the accident. US government emails released to the this week showed the authorities had to track and measure the size of the spill.