The 50p top rate of tax may not be bringing in any income for the Government and could even be costing the Treasury revenue, a leading economic think-tank has warned.
The Institute for Fiscal Studies (IFS) said it is simply the Treasury's "best guess" that the 50p rate on incomes over £150,000 a year would produce some revenue
The finding, contained in a wide-ranging review of the UK tax system, will fuel demands from some senior Tories to scrap the 50p rate introduced by the former Labour government.
Overall, the review led by the Nobel laureate economist Sir James Mirrlees concluded that the current system is "inefficient, overly complex and frequently unfair".
It said that Britain's "poor tax design" contributed to an inefficient housing market, distorted savings and investment decisions and lower levels of employment than need be.
In a series of far-reaching proposals for reform it called for stamp duty to be abolished, VAT to be extended to nearly all spending, and fuel tax to be almost entirely replaced by a comprehensive system of congestion reporting.
However, it is the finding that the 50p rate could be costing the Exchequer income that is likely to attract the most attention.
Chancellor George Osborne has made no secret of his desire to scrap it and many Tories argue that its abolition could help kick-start the stalled UK economy.
However, they face entrenched opposition from their Liberal Democrat coalition partners who insist any tax reduction for the wealthy should be paid for by new measures, such as a tax on high value properties.
The IFS report does not make any recommendation on retaining or abolishing the 50p rate. It does however note: "It is not clear whether the 50% rate will raise any revenue at all... The Treasury's best guess is that the 50% rate will raise some revenue. That is certainly not impossible, but it is certainly uncertain."