In the 1970s, the UK was known as the “sick man of Europe”. Today it seems to be the sick man of the developed world. The IMF forecast this week that Britain would be the only leading economy to shrink this year. Its gloomy outlook was published, by coincidence, on the third anniversary of the UK’s exit from the EU. The Brexit deal is by no means the only reason for Britain’s underperformance, but it is a factor. Finding ways to soften its impact needs to be part of a broader strategy to rekindle growth.