The other day I came across a very interesting tool and way of looking at an economy, the ability to measure the GDP generated yearly against the level of debt taken on by the nation. In other words how has every £ added in debt helped the economy grow?
Unfortunately I could only find this statistic for the USA so I've comprised my own charts for the United Kingdoms public & private debt levels using various public resources (including the 2011 budget).
The first chart belows shows how public level of debt reflect changes in the UKs GDP since 1988, this information was collected courtesy of
UKPublicSpending and the
2011 Budget. The total deficit line (blue) comprises of the economies total borrowings for each year (public and private liabilities) vs changes in GDP and the total public debt line (red) demonstrates the total net government debt vs changes in GDP.

Clearly in the 2008/9 recession there was a negative change in GDP therefore every £ spent results in a negative return, this is not to say that the spending was the cause of the recession (although there is probably some truth in that) just an analysis of the return for every £ added in debt. Interestingly both of the data lines show downward trends towards 0 (where adding debt is no longer adding towards GDP growth), with total yearly debt reaching the line before total government debt. In fact the economies total liabilities, including private debt (mortgages, business loans, etc), has shown a much more consistently downward momentum than total government debt.
This diminishing return on borrowing may be down to a number of factors; the increased availability of cheap loans diverting resources to less productive areas of the economy, loss of purchasing power in the £ (currency devaluation/inflation) or perhaps even market saturation with credit. If the total yearly economic deficit line is to be believed this year we will find that more borrowing (in both public and private sectors) is actually going to start negatively affect the economy (another recession), however the BoEs low interest rates continue to encourage borrowing over saving.
This above chart shows the change in GDP compared to total public debt since 1921 with a 15 year moving average and the % change in debt levels (deficits & surplus). Interestingly not since the Great Depression and WW2 have we seen the GDP Change/Debt ratio dip below the 0 mark and never before has it coincided with such a huge leap in government debt. Even in the recessions of the 80s and 90s (where you can see a nice bubble), despite large declines in the return on borrowing, we never fell close to the 0 return mark. However in 2008 as borrowing doesn't seem to have had such a positive effect stimulating GDP as it had in previous years the recession pushed us below the 0 return line and into negative GDP for the first time since 1945.
So what does all this tell us? From the looks of things we are moving into quite uncharted territory, we have worked up a substantial debt over the past 40 years (constant percentage increases in debt) and our trend lines suggest that the ability to borrow and stimulate growth has been and continues to diminish. It's quite difficult to predict exactly what this all means, the next few years will show us whether 2008 was a blip or the start of a new trend; where borrowing in either the public or private sector struggles to produce sizeable levels of growth. When you combine this with the wider picture; currency devaluation, trade deficits, food shortages and the other stuff BoE economists have been "holding at bay" for years, it certainly looks like we are in for a rough ride.