Forecasting Brexit is still the same old mug’s game it always was. But the probability of a no-deal Brexit has risen dramatically since last week’s summit of European leaders. That scenario can be avoided, for now, if Theresa May were to be ousted as prime minister. The EU would always accept a request for a further delay in such a situation. But it would still insist Britain organise European Parliament elections on May 23 — the UK cannot be allowed to undermine the legitimacy of the European Parliament while it is negotiating its way out. And a new leader would...