Source: The Economist.
This NBER data series q10021 appears on the NBER website in Chapter 10 at http://www.nber.org/databases/macrohistory/contents/chapter10.html.
NBER Indicator: q10021
Release: NBER Macrohistory Database
National Bureau of Economic Research, All Private Applications for Great Britain [Q10021GBQ431NNBR], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/Q10021GBQ431NNBR/, November 28, 2015.