Professor Geoffrey Maitland says BP report leaves questions

BP says no single factor caused the oil spill in the Gulf of Mexico, the worst ecological catastrophe in recent US history.

Instead, "a sequence of failures involving a number of different parties" led to the explosion which killed 11 people and caused the leak.

The report, published on the company's website, criticised the cementing of the well and repeated previous criticism of the blow-out preventer.

The BBC's Tim Cox spoke to Professor Geoffrey Maitland, chair of energy engineering at Imperial College London. He asked him if the cement job was to blame.