Whatever happened to "an old tax is a good tax"?

James Cloyne of University College London has an interesting new paper on the effects of taxes on growth: "What are the effects of tax changes in the United Kingdom? New evidence from a narrative evaluation." The narrative evaluation in question, provided in an exhaustive companion paper, summarizes British budgets going all the way back to 1945. The purpose of the narrative, in part, is to try to judge whether the tax changes reacted to macroeconomic circumstances, so that the statistical relation between taxes and GDP would be contaminated by feedback effects. Cloyne finds a number of cases where tax cuts were introduced more or less independently of macro conditions, including four periods of "supply-side reform" (1957-8, 1970-3, 1983-4 and 1995-6, all under Conservative governments). Cloyne judges that subsequent changes in GDP were pure tax effects. He finds that these effects are large: "Output increases by around 0.6 per cent on impact, rising to 2.5 per cent over 3 years. This implies that tax cuts stimulate above trend growth for over three years" (p. 27).

What's also intriguing is that Cloyne identifies 2500 discretionary tax changes between 1945 and 2009, an average of 39 per year. Whatever happened to the idea that an old tax is a good tax?