The number of economists who think the NBER study is flawed is clearly growing:
Pro-Brexit economist Julian Jessop;
https://julianhjessop.substack.com/p/what-the-nber-gets-wrong-on-the-economic
And now economists at Bloomberg have questioned the modelling. NB I recall that Bloomberg gave a £250,000 donation to the Remain campaign in 2016 for context;
https://www.politico.eu/blogs/on-media/2016/05/bloomberg-gave-250000-to-remain-campaign/
June 2026
Leaving the European Union has cost the UK 2% to 4% of forgone economic output but almost half can be recovered by improving trade with the bloc, according to analysis by Bloomberg Economics for the 10-year anniversary of the Brexit referendum...
Bloomberg Economics used a variety of models to calculate its central estimate of the cost to date. It found the damage was far smaller than the 6% to 8% of GDP hit set out in a recent and widely read National Bureau of Economic Research paper. [Although I would counter the claim that the NBER research paper was widely read - the headline was widely read].
Using a “doppelganger” model like the NBER to build an alternative growth path assuming the UK had remained in the EU, Bloomberg Economics said the damage would be 9.6%.
However, it said the estimate is misleading because the NBER doppelganger includes Ireland, where growth has averaged 7% a year since the 2016 referendum thanks to its low-tax strategy, and [the doppelganger] is heavily weighted to the US, which unlike the UK “wasn’t hit by an energy shock in 2022, has benefited from significant fiscal stimulus and is seeing the benefits of AI investment.”
Stripping out Ireland reduces the hit to about 6% and adjusting the US growth trajectory to reflect pre-2016 levels of outperformance lowers the impact further to 3.4%. Alternatively, using the World Trade Organization’s Global Trade Model, capturing the impact of higher trade barriers, points to a 2.5% long-term hit, Bloomberg Economics said.
https://www.bloomberg.com/news/articles/2026-06-09/how-the-uk-s-options-for-rebuilding-ties-with-europe-stack-up