Could a row over steel blow up the Tory party?

When Boris Johnson was campaigning for Brexit, he placed much importance on World Trade Organisation rules. The WTO, he’d argue, had an internationally-recognised free trade rule book – which was ready and waiting to be used as a substitute to the European Union system. This is why he could face some very difficult questions next week if he decides to extend tariffs on steel imports in a way that some think flout WTO rules.