Mr. Eddie Casey:

A few years ago, we did a paper on whether we could forecast corporation tax better than the Department was doing at the time. We looked at almost ten different models and found that none of them was any good as it is a really unpredictable revenue source and the most volatile of the main tax heads, with the largest forecast mistakes year in, year out. It is also really concentrated so when an individual firm has a patent which runs out, or there is some other shock to profitability, it can lead to big changes in corporation tax receipts in a given year. As Mr. Tutty said, the international tax environment can also change and these are things that are beyond our control. The key is not to build up a reliance on this one tax head by spending it in a long-lasting way.