LONDON • If all goes according to plan, British Prime Minister Theresa May will face the serried ranks of 650 Members of Parliament in London later today to reveal to an increasingly apprehensive nation her new plan designed to take Britain out of the European Union.

There is not a moment to lose. Having spent two years negotiating a treaty for Brexit - as the process of Britain's divorce from the EU is universally known - only to see it thrown out by MPs in the largest parliamentary defeat ever suffered by a British government, Mrs May now has barely two more months to invent another treaty that is acceptable to legislators, or she risks having Britain simply crash out of the union, with catastrophic implications for everything ranging from the country's food and medicine supplies to its transport infrastructure to its international relations.