Has the growth of real GDP in the UK been overstated because of mis-measurement of banking output?

If official figures overstated the growth of banking output in the UK in the recent boom, does this mean that GDP growth was overstated too? The answer is no. It is truer to say that if banking output was overstated then the output of some other industry or industries must have been understated, leaving GDP relatively unaffected. The reason is that the Office for National Statistics measures the real growth of GDP primarily from the expenditure side. And from the expenditure side most of the problematic part of banking output drops out since it constitutes intermediate consumption not final expenditure. Consequently, the effect of any mis-measurement of banking output on GDP growth in the boom of 2000-2007 is likely to have been small: GDP growth might have been overstated by about 0.1% p.a.