The Prince of Wales lobbied for one of the world's leading architects to be dropped from a £500m office and shopping complex beside St Paul's Cathedral so one of his preferred designers could take over, the Guardian has learned.

The developer who commissioned the Paris-based Jean Nouvel to design One New Change has revealed that the prince called for an alternative architect to be considered for the sensitive site yards from Christopher Wren's masterpiece.

In a private letter to Land Securities, one of Britain's largest commercial developers, the prince made clear he felt the firm had got its design approach wrong. He said he was concerned that the design should "allow St Paul's to shine bright" and offered his own architectural advisers, who prefer traditional forms, to help.

"He wrote to me at the time we selected Nouvel and suggested we should meet his preferred architects," said Mike Hussey, then London director of Land Securities. "He hadn't seen the scheme, he just complained about the selection of the architect. He didn't want a modernist."

Charles's intervention, in a letter sent in 2005, emerged from a wide-ranging investigation by the Guardian into the extent of his sometimes hidden role in shaping Britain's skyline.

Amid concerns that his hands-on involvement in planning and architecture may exceed his constitutional role, it has also emerged that:

• His aides regularly scrutinise plans by major architects including Sir Terry Farrell, Sir Richard MacCormac, John McAslan and Alan Baxter who work on some of Britain's largest building projects.

• He told English Heritage's chairman to urge cabinet ministers to block a £200m development at Smithfield Market in London. It was rejected and his aides have now been asked to endorse new plans.

• His architecture charity is involved in plans for more than 17,000 homes across Britain – more than Persimmon, one of the country's largest house builders, built last year.

There were renewed concerns last week about the prince's influence when five design firms allied to his approach to architecture were selected to draw up draft plans for the Chelsea Barracks site after he successfully persuaded the Qatari developers to sack Richard Rogers. Like Lord Rogers, Nouvel is a winner of the Pritzker prize, architecture's version of the Nobel, as well as the Royal Gold Medal, Britain's highest accolade for an architect. The prince routinely opposes modernist architecture and advocates traditional styles based on historical precedents.

Sunand Prasad, president of the Royal Institute of British Architects, described the intervention at One New Change as "brazen" and "pernicious" and last night called for him to "step back".

"The prince has an unusual amount of power which, under our constitution, is not designed to be used to interfere with the running of everyday affairs in this country for the simple reason that the prince is not accountable," said Prasad. "This is a dangerous course to go down. There was an open competition for this building and then along comes somebody with special powers seeking to influence the outcome in a blatant intervention."

Clarence House confirmed the private letter was sent in 2005 following Nouvel's appointment. The architect had won the commission in an international competition and the designs had been submitted to the Corporation of London planning authorities. Hussey, a leading patron of modernist architecture, decided the prince's suggestion was "not appropriate" and wrote back to decline the offer.

A spokesman for Clarence House said Charles was concerned to retain St Paul's "inspirational" status on the London sykline, but declined to comment further on the prince's private correspondence.

His aides believe the prince is entitled to share his views on the built environment. They defend his right to intervene over developments close to buildings or sites of national importance as he has done over the National Gallery on Trafalgar Square, the Royal Hospital at Chelsea, and Paternoster Square, also beside St Paul's.

Nouvel was unavailable for comment.