From the executive summary:
- The 50 per cent additional rate of income tax was introduced on 6 April 2010. It was the first increase in the highest rate of tax in the UK for over 30 years, and was expected to yield around £2.5 billion.
- This report provides the first comprehensive ex-post assessment of the additional rate yield using a range of evidence including the 2010-11 Self Assessment returns.
- This analysis shows that there was a considerable behavioural response to the rate change, including a substantial amount of forestalling: between £16 billion and £18 billion of income is estimated to have been brought forward to 2009-10 to avoid the additional rate of tax. This behavioural response is entirely legitimate, and difficult to prevent using anti-avoidance legislation.
- The modelling suggests the underlying behavioural response was greater than estimated previously in Budget 2009 and in March Budget 2010, decreasing the pre-behavioural yield by at least 83 per cent. This result is also consistent with that contained in the Mirrlees review, and suggests the additional rate is a highly distortionary form of taxation. Although there is uncertainty around these estimates, sensitivity testing demonstrates that is difficult to construct a plausible outcome consistent with a yield estimate as high as those original forecasts. The conclusion that can be drawn from the Self Assessment data is therefore that the underlying yield from the additional rate is much lower than originally forecast (yielding around £1 billion or less), and that it is quite possible that it could be negative.