How he made his views known over tea at Clarence House

The meeting between Prince Charles and the Emir of Qatar that took place at 6pm on 11 May last year was always going to be awkward. The Sandhurst-trained Sheikh Hamad bin Khalifa al Thani had long enjoyed a warm relationship with the heir to the British throne but more recently something had come between them, namely 12.8 acres of the most prime real estate on the planet.

As the Emir and his second wife, Sheikha Mozah, took tea with the prince amid the stuccoed splendour of Clarence House, this cosy get-together between two royal dynasties of contrasting fortunes moved to the delicate matter of Charles's implacable opposition to the £3bn scheme by the oil and gas-rich emirate's development company, to transform the site of Chelsea Barracks into 17 glass and steel apartment blocks designed by Lord Richard Rogers.

Accounts of the vigour with which the prince, who had described the proposals as "brutalist", made his case vary widely. Sir Michael Peat, the prince's private secretary, noted with the sober understatement of a courtier: "The Emir was surprised by Rogers' design for Chelsea Barracks and said he would have them changed."

Another version suggested a more lively encounter, describing how Charles had "pissed in [the Emir's] ear about how awful the scheme was" and caused the 58-year-old monarch to "go mental" at the head of Qatari Diar Real Estate Investment, the state-owned development company which has helped transform the Middle Eastern emirate into the world's biggest property investor.

Either way, the aftermath of the encounter was dramatic. Within a month of the chat on the sofas at Clarence House, the planning application against which Charles had fought an eight-week campaign of intensive lobbying – starting in March 2009 with an outspoken letter to the Qatari prime minister – was withdrawn days before it was due to go before the planning committee of Westminster City Council.

Whether the proposals were pulled off the table as a direct result of the prince's interventions went to the heart of the legal battle partially lost yesterday by Qatari Diar in London's High Court.

The complex contractual dispute succeeded in bringing together an unlikely cast of royalty and tycoons, ranging from the billionaire plutocrats of a once-impoverished desert kingdom to Christian Candy, whose property company, CPC Group, won its claim that Qatari Diar had breached a contract by withdrawing the plans.

But more than anything, the proceedings in the Royal Courts of Justice have shone an uncomfortable light into just how two of the more influential aristocratic powerbrokers in the world – Prince Charles, who has made the resurrection of "old-fashioned" architecture in Britain a personal crusade, and the Emir of Qatar, where the discovery of the world's third largest reserve of natural gas has produced a vast sovereign wealth fund – use their considerable sway when it comes to issues of public interest.

Critics of Prince Charles, among them some of the world's leading architects from Lord Foster to Renzo Piano, accused him of using his "privileged position" to "skew" the democratic planning process via his meeting with the Emir and representations to elected officials, including the deputy mayor of London.

From the outset the heir to the throne made little secret of his determination to see off the 548 executive flats and social housing units proposed by Lord Rogers, with whom the prince has had several spats about the virtues of modern architecture.

The High Court heard that John Ward, the chief operating officer of Qatari Diar in the UK, had been told by Michael Peat that the prince was "going to fight to the finish" against the proposal. The indignation of Charles about what he views as the steady scarification of Britain's cityscapes with buildings lacking his preferred neo-classical lines was first brought to the attention of the Qataris on 1 March last year, in the shape of an idiosyncratic missive from Clarence House to Sheikh Hamad bin Jassim, the Qatari prime minister, head of his state's £45bn sovereign wealth fund and first cousin of the Emir.

In the letter, amended with thick ink underlinings of certain words by its author, a strident Prince Charles complained about the march of "brutalist" architecture taking over "the very soul of our capital city".

Admitting that he was being "interfering", the prince said he was urging Sheikh Hamad to "reconsider" the plans for the Chelsea Barracks site, bought by a coalition led by Qatari Diar for £958m in 2007 from the Ministry of Defence – making it the most expensive land deal in London.

Qatari Diar insisted that, despite his meeting with Charles, the Emir was not involved in the decision to withdraw the plans. But Mr Candy, 35, saw matters differently, saying there was evidence that the absolute monarch, who had previously spoken to the then global chief executive of Qatari Diar, Ghanem bin Saad, just five times in the previous six months, personally intervened immediately after the meeting with Prince Charles.

In an email on 21 May, Mr Candy provided an account he said he had been given of the meeting between Charles ("PoW") and the Emir. Mr Candy wrote: "When the Emir was in the UK and spoke to PoW, the PoW pissed in his ear about how awful the scheme was. The Emir then went mental at Ghanem, telling him how awful the design was, and they must witdraw ASAP."

Such was the anxiety of Qatari Diar to accommodate the objections of Charles, the company offered to revise the designs once planning permission had been obtained. But this was not enough for the determined prince, who must now be a happy man. Last year a new set of plans was unveiled by the architects who are known to have the prince's approval.