That report seems to estimate the 'long term' loss of GDP compared to our having stayed in at about 4%. If 'long-term' means 4% over 15 years, then if memory serves it is consistent with the pre-referendum 'project fear' Treasury estimations.
It of course entirely depends on the policies of successive governments here (there will have been another three by then), as well as events in mainland Europe. Quite apart from the inevitably destructive dynamics of the Euro, the EU's regulatory inclinations and complex, increasingly irritable decision making processes, already ensure that the bloc's growth lags increasingly behind the developing countries and the US.
I don't think your link indicates news, more confirmation of existing opinion.