In a rare interview with a foreign journalist, a senior Angolan official last year submitted himself to questions about a range of subjects, including the thorny issue of the notorious lack of transparency in the oil industry. But when the conversation moved to Angola’s decision to join the Opec oil cartel he gave the distinct impression of wanting to bring the interview to an end.

Then after a pause and a reminder that he was speaking “off the record” he launched into a response, and left little doubt that, given Angola’s booming oil production, he thought the decision to submit to an Opec quota was a mistake.