Over the last few weeks, most economists have been trying to work out how we can deal with the crisis in the eurozone. Will the banks go bust if there is a sovereign default? If so, should the governments bail them out? The EU now comes along with a clever idea to take £50bn a year out of the financial sector through a transactions tax. The likelihood is that, as transactions tax before them have failed to raise revenue, this will fail too - as markets migrate to other parts of the world.