Speaking on BBC Radio 4's Front Row programme Ruth Reed, the first woman president of the institute, said: "It is unfortunate if anybody uses their position in public life to exert undue influence on a democratic process such as planning.
"There appears to be evidence that he has written behind the scenes both about planning applications and also about the appointment of particular architects, which would be an abuse of his position, definitely."
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Clarence House has declined to comment on the claims.
Earlier this year, Prince Charles intervened in Lord Rogers' scheme to redevelop London's Chelsea Barracks urging a rethink on the modern design.
In a speech before the RIBA in May, he described much of the design as "flawed", preferring an alternative classical design by architect Quinlan Terry.
Around 25 years ago, he famously attacked a proposed National Gallery extension calling it "a monstrous carbuncle on the face of a much-loved and elegant friend".
Last month it was reported that Charles had unsuccessfully tried to intervene in plans to build a modernist building next to St Paul's Cathedral.
(GK/KMcA)
