As predicted, and generally expected, Isil set fire to the Mishraq Chemical plant and sulphur mine 30 km south of Mosul on Thursday last week as they fled towards the city. To date, up to nine people have died and around 1,000 have been injured, including foreign journalists.

The toxic cloud, which includes deadly sulphur dioxide and hydrogen sulphide, combined with residue from burning oil wells, is a potentially fatal cocktail for those caught in the open or without gas masks.

It currently stretches 20-30 km to the south over sparsely populated ground, but if the wind changes to blow to the east, as it usually does at this time of year, there is a slim chance that the Kurdish capital Erbil, 60 km away, could come under threat.