Six months on from the formal end of western sanctions the international financial community’s reluctance to do business with Iran is rapidly breaking down.

While western countries and their Gulf allies did their best to isolate Iran from trading during the 2012-15 period of heightened sanctions, one area where Tehran proved more resilient was in continuing to export its oil to select customers.

Oil has always been the lifeblood of the Iranian economy but in this case its exportation...