Simon Wren-Lewis claims the Brexit slowdown is about to begin because its negative effect on the economy is no longer masked by unusually strong consumption. Hence, GDP is going to take a hit.
The thing is: all the effects the Brexit vote could conceivably have in the short-run pertain to aggregate demand (AD). Since AD is controlled by the BoE, there is no reason to assume that Brexit will have any short-run consequences on GDP – as I already pointed out immediately after the Brexit vote.
One may argue that at the Zero Lower Bound (ZLB) and under strict inflation targeting, the central bank might lose this control. But since monetary policy in the UK is not even at the ZLB, this theoretical possibility does not apply in the case of post-Brexit Britain.
In general, if the central bank is doing its job properly, any slow-down or reduction of GDP caused by demand-shocks is impossible to predict ahead of time.
Why has this basic fact been ignored by so many economists in the case of Brexit?
Well, most of the economists who have been predicting a negative effect of Brexit on GDP in the short-run believe that Brexit will have a negative effect on the long-run supply side of the British economy. Whether the long-run effect of Brexit will be negative or positive is debatable but taking a pessimistic view is certainly not inherently flawed.
Since economists are human and few humans are immune to the passions involved in political arguments, I guess that, being of the conviction that the long-run effects of Brexit will be negative, these economists have been tempted to loosen their intellectual standards and to sex up their arguments by making gloomy predictions about the short-run as well.
That so many economists have been making these predictions may make them seem respectable. It doesn’t make them well-reasoned or correct.