The Prince of Wales should be stripped of control of the Duchy of Cornwall which gives him almost £12 million a year, MPs demanded today.
Prince Charles's financial arrangements were criticised by a high-powered House of Commons committee, including Birmingham MP SiUn Simon (Lab Erdington).
Mr Simon said: "This is a centuries-old stitch-up which has finally been rumbled."
The £463 million Duchy of Cornwall was created by Edward III in 1337.
It covers 56,000 hectares, including holdings in Herefordshire, and provides an annual income of £ 11.9 million.
But the Commons Committee of Public Accounts hauled in the Duchy's managers for questioning, when they conducted an inquiry into the Prince's finances earlier this year.
During a stormy evidence session in Parliament, MPs including Mr Simon clashed with Bertie Ross, the Duchy of Cornwall's secretary, who refused calls to submit the estate's accounts to independent scrutiny.
Today the MPs published their findings, and demanded major reforms.
They warned that there was a conflict of interest between the Prince's duty to protect the Duchy for future generations, and his immediate interest in maximising profits.
The solution was to strip him of any direct involvement in managing the Duchy, they said.
This would bring the Duchy of Cornwall more in line with the Duchy of Lancaster, which provides an income for the Queen but is not managed by her.
The MPs also called for an inquiry into whether the Prince actually needed all the money he received - saying the last time anyone looked into this was 400 years ago.
They called for the Duchy's accounts to be made available to independent auditors before being presented to Parliament for approval, and for more information to be included.
And they demanded an explanation from the Treasury as to why the Duchy paid no corporation or capital gains tax.
The harsh conclusions will put the MPs on a collision course with Gordon Brown, the Chancellor, who has built close ties with Charles through joint work to help the young, budding entrepreneurs, the developing world and on regenerating cities.
But they were defended by Mr Simon. He said: "Hopefully this report will be the beginning of the end of this stitchup. It wasn't fair in the 14th century and it's not fair now.
"The Duchy's profits are quite clearly public money, whatever stories they tell us."
The Committee's report warned that it was sometimes unclear what belonged to the Prince and what belonged to the Duchy.
In 1998 the Duchy paid the Prince £2.3 million for timber grown on Duchy land, which had previously appeared as an asset on the Duchy's balance sheet. Highgrove House was bought by the Duchy and then rented to the Prince, but the rent was effectively returned to the Prince as part of his income from the Duchy, the MPs said.