I know that a lot of tax is fiddled out of the exchequer by dodgy practices: people claiming to be subcontractors when they are actually employees, overclaiming of expenses, personal use of company assets, cash-in-hand payments, use of off-shore accounts etc. There must be an estimate of the total lost this way. How much is it? More to the point, if all these practices were eliminated (together with the costs of trying to police them) how much could the basic rate of tax be reduced and still allow the total tax revenue raised to be the same?