Jim, your link to the 'Relevant Experts' tells us:
The International Monetary Fund has strongly defended its gloomy forecasts for the UK after Brexit, saying pre-referendum warnings of slower growth were coming true.

Christine Lagarde, the fund's managing director, said the vote to leave the EU in June 2016 was already having an impact and Britain's weaker growth this year was in contrast to accelerating activity in the rest of the world.

Speaking at the Treasury as the IMF announced the results of its annual health check of the UK economy, Lagarde hit back at those who lambasted the fund when predictions of an immediate post-referendum recession failed to come to pass.

"We feared that if Britain decided to leave, it would most likely entail a depreciation of sterling, higher inflation leading to a squeeze on disposable income and a reduction in investment," she said.

Basically "We were wrong before when we predicted calamity, but you'd better believe us now because we believe we're right".

Chicken Little comes to mind.