Larry Elliott, writing for The Guardian, makes some important points in this article.

The past few years have seen numerous examples of economic and political forecasts being proven entirely wrong.

It's frowned upon to ridicule 'experts', but in the case of economics, the so-called experts make a rod for their own backs when they treat economic forecasting as a hard science, rather than a delicate art form.

Elliott points out in this article that Brexit is a unique event. Economic models don't tend to work particularly well in the face of big shocks.

He also reminds us of the garbage in, garbage out principle. Economic forecasts ahead of Brexit were tainted by political viewpoints; all of those highly respected economists wanted to maintain the status quo, especially those in receipt of EU funding.

Take any prediction about the future with a liberal pinch of salt. When everyone is saying the same thing is going to happen, consider the alternative as a possibility.