Senior Rio Tinto executives had conceded by May 2012 that constraints on transporting coal out of Mozambique had delivered a "huge value loss" to the miner's fledgling coal business there, which it did not write down until the following year.

The latest revelations came in a 2012 email sent by Rio's then managing director of Mozambique Coal Eric Finlayson, who described the Mozambique government as being an "autocratic" regime afflicted by "high level corruption".