The national consensus holds that the discoveries of huge offshore natural gas fields in recent years amount to an economic revolution, one that will put the economy on easy street for generations to come. A leading British energy expert, however, says it’s an illusion.  Exporting gas as LNG [liquefied natural gas] is very expensive. Israeli gas isn’t competitive enough to compete with LNG from other countries,” says Nick Butler, one-time senior energy adviser to former Prime Minister Gordon Brown, and former vice president for strategy and policy development at British Petroleum Group, in an interview with Globes’ Hedy Cohen.