A Norfolk landowner introduced the Prince of Wales to an offshore company in which his private estate invested millions of pounds, it has emerged.
Hugh van Cutsem, a millionaire banker and horse breeder who died in 2013, met Prince Charles at Cambridge University.
The Paradise Papers leak has uncovered documents showing the Prince of Wales lobbied for a change to two climate change deals after investing in an offshore carbon credit trading company, of which van Cutsem was a director.
The Duchy of Cornwall paid 113,500 dollars (£58,000) in 2007 for 50 shares in the Bermuda-registered Sustainable Forestry Management Ltd (SFM) in 2007.
SFM traded in credits from tropical and subtropical forests, but these type of credits were largely excluded from the EU's Emissions Trading Scheme (EU ETS) and the Kyoto Protocol.
Four months after the share purchase, details of the company's efforts to lobby for amendments to the two treaties were sent to the Prince, minutes from a board meeting suggested.
The documents were apparently sent to Charles at the request of van Cutsem.
Charles criticised the EU ETS and the Kyoto Protocol in speeches he gave shortly after receiving the papers, the reports said.
In October 2007, he launched the Prince's Rainforest Project, with the aim of 'increasing global recognition of the contribution of tropical deforestation to climate change and to find ways to make the rainforests worth more alive than dead'.
He again criticised the two agreements in a speech to mark the launch.
Neither the EU ETS or the Kyoto Protocol were changed as a result of the Prince's lobbying, the BBC said, adding it had been unable to find public criticisms of the two accords made by the Prince before 2008
The Duchy of Cornwall sold its shares in SFM in 2008 for 325,000 dollars (£246,000), according to the leaked papers, almost tripling its investment.
The papers also showed the Duchy of Cornwall made offshore investments totalling £3.9 million in four funds in the Cayman Islands in 2007, the BBC said.
This is legal and there is no suggestion the Prince received any tax benefit as a result of the investments in either SFM or the four funds based in the Cayman Islands.
A spokesman for the Duchy of Cornwall said: 'The Prince of Wales does not have any direct involvement in the investment decisions taken by the Duchy.
'These are the responsibility of The Duchy itself. The Duchy of Cornwall's accounts are independently audited and presented to Parliament every year. The Prince voluntarily pays income tax on any revenue from The Duchy.'
Who was Hugh van Custem?
Hugh van Cutsem inherited his father's stud Northmore Farm in Exning near Newmarket, Suffolk in 1976. He also owned a 4,400-acre estate in Breckland, best known for its private wild game shoots.
For several years the van Cutsems were Sandringham neighbours of the Royal family as leaseholders of Anmer Hall. After the lease expired, the van Cutsems moved into a magnificent new neo-Palladian country house on their own estate at Hilborough, near Swaffham.
He was a friend of Prince Charles since university. His son Edward, whose godfather was Prince Charles, was a pageboy at the wedding of Charles, Prince of Wales, and Lady Diana Spencer in 1981.His granddaughter, Grace van Cutsem, was a flower-girl at the wedding of Prince William and Catherine Middleton in 2011.
His son, William van Cutsem is Prince George's godfather and is a director at Pigeon Investment Managment Ltd in Bury St Edmunds.
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