As a result, some Spanish regions where pre-tax income per head is lower than in Catalonia end up with higher post-tax income.

ECONOMIST: Spain and its regions

Tax on oil and gas production would also have given an independent Scotland a higher tax take per head over the three decades.

BBC: Total's Elgin platform

Ms Sturgeon, giving the final key speech of the conference, said that for every one of the last 30 years Scotland had generated more tax revenue per head than the UK as a whole.

BBC: Nicola Sturgeon

Compared with France, Britain in the 1790s already had a bigger manufacturing base, a higher income per head and hence a tax base wide enough to pay for 22 years of conflict that led to the emperor's Waterloo.

ECONOMIST: British manufacturing