Prince Charles and Sheikha Mozah, second wife of the Emir of Qatar Photo: ARTHUR EDWARDS

The Qataris accuse the Candys of saying one thing in correspondence with them and another in internal emails circulated among CPC senior staff and which now form part of the case. Photo: EDDIE MULHOLLAND

In one corner will be the Qatari royal family accused of reneging on a deal to build a series of glass and concrete apartment blocks to be sold to some of the world’s wealthiest people.

In the other will be Christian and Nick Candy, property developers to the uber-rich, who claim the billionaires of Qatar owe them £81 million.

And looming large in the court will be the presence of the Prince of Wales, the arch-critic of modern architecture, who will not give evidence but who nevertheless played a starring role in preventing the ‘brutalist’ Chelsea Barracks towers from ever being built.

The Sunday Telegraph has seen legal documents which will show how each side will blame the other in a court battle that could cost the loser, with legal fees thrown in, more than £100 million.

Among the hundreds of pages of claim and counter-claim are emails and other documents showing how the Prince of Wales succeeded in persuading Sheikh Hamad bin Khalifa Al Thani, the Emir of Qatar, that a scheme designed by Lord Rogers, the Labour peer and architect, was “awful” and should not be built.

The Emir, over a civilised cup of tea at Clarence House, with his glamorous wife also present, readily agreed. A month after that meeting in May last year, Qatari Diar, the company which owned the land, had withdrawn its planning application for the towers.

It was a move that triggered the legal action that culminates in the start, tomorrow, of a trial expected to last two weeks. Christian Candy’s company, CPC Group, is suing for breach of contract. The Candys will argue that had it not been for Prince Charles’s objections the plans would have been approved and they would have been entitled to an £81 million success fee.

But Qatari Diar has struck back. The company denies it breached the contract and refuses to pay the money, arguing that the scheme was doomed to failure at the planning stage and would have been rejected either by Westminster City Council or, later, by Boris Johnson, the London mayor.

Counter-claim documents seen by The Sunday Telegraph allege CPC Group acted in ‘bad faith’ by using Prince Charles’s intervention to their advantage to ‘implement a strategy of encouraging Qatari Diar to withdraw’. Qatari Diar will argue that the Candy brothers wanted this to happen because they believed it would be the fastest way to collect £69 million, which would have been due in compensation if the contract were broken.

The Qataris accuse the Candys of saying one thing in correspondence with them and another in internal emails circulated among CPC senior staff and which now form part of the case.

The Candys deny acting in bad faith and argue they did their best to get planning permission but were thwarted by a growing campaign against their scheme.

There had been rumblings of local discontent ever since Lord Rogers’ plans were unveiled in the middle of 2008 with complaints from such luminaries as Lord Stockton.

But the story erupted when it was leaked to the press that Prince Charles had written a letter on March 1 last year to Qatar’s prime minister Sheikh Hamad bin Jasim, who also happens to be chairman of Qatari Diar, voicing his “particular concerns” for “one more brutalist development”. The letter, revealing Prince Charles’s passionate despair over the modernist style of architecture, will form part of the evidence in the case.

The letter – described by Qatari Diar in their submissions as a ‘hand grenade’ which CPC knew would ‘almost certainly’ result in the planning application being rejected – was at first largely ignored.

The Sunday Telegraph understands that a neutral reply was sent by Qatari Diar politely acknowledging the letter but refusing to take sides. It is thought another letter was drafted, defending the scheme, but was never sent. The existence of the letter was subsequently leaked prompting a furore.

Then on 11 May, Prince Charles invited the Emir and his second wife Sheikha Mozah Bint Nasser Al Missned, who were in the UK to open a gas terminal in Wales, for tea at Clarence House.

Prince Charles and Sheikha Mozah have been close friends for years, having both been involved in a series of charitable causes. She is described in court papers as a “regular visitor”. The Emir is emerging as a powerful figure on the world stage. Qatar, with huge reserves of natural gas, now has large stakes in companies such as Barclays, Volkswagen and Sainsbury’s. Earlier this month, Qataris announced they were buying Harrods for £1.5 billion.

Minutes of the meeting recorded by Sir Michael Peat, the prince’s private secretary and which will also be used in the court case, state: “The emir was surprised by the Rogers’ designs for Chelsea Barracks and said that he would have them changed.”

Christian Candy had a slightly different take. Having got wind of the meeting and having been briefed about it, he subsequently sent a candid internal email, which also forms part of the evidence, with his own colourful interpretation of what had taken place. ” … when the Emir was in the UK and spoke to PoW [Prince of Wales],” he wrote, “The PoW p—-d in his ear about how awful the scheme was. The Emir then went mental at Ghanim [Ghanim bin Saad al-Saad, the CEO of Qatari Diar], telling him how awful the design was and that they must withdraw ASAP”.

A month later Qatari Diar had done just that and Lord Rogers’ scheme, which would have cost £3 billion all in, was dead in the water. In its place Qatari Diar have resubmitted a new, low-rise plan by the firm that built the extension to the Royal Opera House, in London’s Covent Garden.

Behind the scenes over the course of this past 12 months, there have been leaks and briefings as each side has tried to gain an advantage over the other.

Such is the enmity on both sides that hopes of a last minute settlement on the steps of the court remain slim, despite the huge costs of conducting the case.

A source close to the Candy brothers said: “This is about a contractual obligation. The Qataris have ridden rough shod over their contractual obligations.”

Back at Clarence House, the Prince of Wales and Sir Michael Peat will be glad not to have to give evidence. A source there said: “Prince Charles is entitled to his private opinions. Any dispute between the Candys and the Qataris is for them to resolve, not for us. The Prince knows the Emir and his wife extremely well and as a matter of course they would have called on him anyway in May last year. The meeting was not about any one specific subject.”