The war in eastern Ukraine is rumbling on. Russian-backed separatists still control much of the eastern industrial region known as the Donbas. But despite the shelling, trade in coal and other goods was continuing across the frontline – until a group of Ukrainian activists opposed to President Poroshenko decided to put an end to it by organising a blockade. The move threatens the region with economic collapse and is proving highly controversial. Our correspondent Gulliver Cragg reports.