The blowout preventer's control pod, which was also originally connected to the lost rig, has been taken up to the Q4000, where it has been tested and attached to new cables.

ECONOMIST: The Gulf oil spill

The control pod will open the valves that allow the drilling mud to be forced into the well.

ECONOMIST: The Gulf oil spill

Mr Wells says that once the control pod has been reinstalled on the blowout preventer and the manifold is attached to the Q4000, the top kill could start.

ECONOMIST: The Gulf oil spill