Guardian: BP ordered the owner of the Deepwater Horizon rig, whose explosion led to the worst environmental disaster in US history, to overhaul a crucial piece of the rig’s safety equipment in China, the Observer has learnt. The blow-out preventer – the last line of defence against an out-of-control well – subsequently failed to activate and is at the centre of investigations into what caused the disaster. Experts say that the practice of having such engineering work carried out in China, …