In 1909 the United Kingdom Government introduced “super-tax”, which was an additional income tax levied on top incomes. This provided information on the distribution of total incomes that had not previously been available on a regular basis, since under the ordinary income tax, the authorities did not know the total income of individuals, which could be the subject of several separate assessments. Super-tax remained in existence until 1972, by which time other income tax sources (the Survey of Personal Incomes) were in place to allow the series to be continued. The aim of this paper is to examine what can be said from the published super-tax statistics about the evolution of top incomes in the United Kingdom. The paper spells out the limitations of the super-tax information, and the problems in establishing control totals for total population and total income, but argues that it provides a unique source of evidence about the distribution of top incomes covering virtually the whole of the twentieth century.
The resulting picture, if blurred in places, allows us to draw broad conclusions about developments over the twentieth century. There is no longer the extent of inequality to be found before the First World War, with the Upper Ten Thousand receiving nearly a tenth of total income. The magnitude of the change may be need to be qualified in the light of fiscal re-arrangement, but there have been distinct periods of equalisation, notably during the two world wars, from 1946–1957 and from 1965–1972. But there is no steady trend. There have been plateaux. Since 1979, we have seen a reversal, with shares of the top income groups returning to their position of fifty years earlier. The equalisation of the post-war period has been lost.