The past week has seen much debate over the 50p rate of income tax. Tax debates often focus on these single, totemic issues - be it the basic rate of income tax, or the tax on a litre of petrol. But, important as these are, they are only small elements of a wider, flawed system. At a time when Britain's economy badly needs a boost, much wider tax changes are now needed.

The most comprehensive review of tax policy in 30 years, the Mirrlees review, published on Wednesday, argues the tax system has to be seen as just that: a system. It must be coherent as a whole, and the various bits need to join up if it is to be fair and efficient. Equally, it must be designed on the basis of evidence - one of the big problems about the debate on the 50p rate. To the extent that we can deduce from past experience, it seems unlikely the 50p rate will raise much. But in truth we simply don't know.

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