Here's a chart from a long piece by Martin Wolf in the FT:

It shows how much GDP per capita (a much better measure of relative national prosperity than basic GDP figures), has deviated from its medium term trend;

What you'll notice is that despite claims by the #Tories that our economic problems are global in character, in this group of states our negative deviation is worse at around 30% reduction;

So what might be the independent variables;

Top of my list:
#Brexit & a decade of Tory rule!