For 21 years allegations of kickbacks have swirled round the biggest arms deal in history - Al Yamamah, the 'dove of peace'
Tornado jets were part of the Al Yamamah deal with Saudi Arabia
Ever since Mrs Thatcher stepped off her plane resplendent in a Tory blue suit and veiled hat to greet the Saudi King and seal the Tornado warplane sale, the story has generated acres of speculation in newsprint and hours of broadcast time.
Rumours about her own son, Mark's role as a broker have featured large in the headlines.
But until Panorama broke the story of secret payments into accounts controlled by Prince Bandar, the former Saudi ambassador to the United States, no journalists had got to the heart of the matter.
We have provided for the first time details of the mechanism involving BAE Systems with the approval of the British Ministry of Defence in the transfer of hundreds of millions of pounds into accounts controlled by Prince Bandar.
It took the Panorama team, myself and colleagues James Oliver and Guy Smith several months of exhaustive research and filming to untangle the threads.
There were many long meetings with our well-placed sources who in this politically sensitive story did not want to appear in our film.
But as always in a tale involving allegations of fraud or corruption the maxim is 'follow the money'.
So that is what we did. It took us to Switzerland, France, Germany and America where we met an ex-secret service investigator - David Caruso.
Mr Caruso had never spoken before in detail before about the Saudi embassy accounts he was asked to look at in 2003 by Riggs Bank - bankers to Prince Bandar and his embassy in Washington.
Mr Caruso confirmed to us that the accounts we were interested in had been used as a personal piggy bank by the Prince.
The probe had started post 9/11 when most of the hijackers turned out to be Saudis and there were suspicions they might have been receiving funding via the Saudi embassy.
No links to terrorism were found but Mr Caruso did identify 'suspicious payments' he told us in some of the accounts.
Amongst them was the Saudi Ministry of Defence and Aviation account which our information indicated might well have been better described as a conduit to Prince Bandar.
An internal Riggs Bank document we obtained showed that the Prince had taken $17 million (£8.5 million) out of this account in the summer of 2003 for a construction project in Saudi Arabia.
Mr Caruso confirmed the investigators had been told it was for a home - or rather a palace for the Prince.
Riggs Bank was never able to get satisfactory answers to their questions about the accounts which contained hundreds of millions of pounds.
So Riggs closed them down and terminated its relationship with Prince Bandar and the embassy. The Prince later told us in a statement the account was for purposes approved by the Saudi Ministry and not for his personal use. The palace he said was an official residence.
Some of the more light hearted moments in making the film occurred when we were introduced to the arcane world of plane spotting.
Spotters all over the globe have monitored the movement of Prince Bandar's luxury Airbus over the years and they were able to give us valuable information about dates and times which helped us put our story together.
Panorama had discovered that travelling expenses for the plane - hundreds of thousands of pounds a year had been paid via BAE and the Ministry of Defence into another of the embassy accounts in Washington.
Jane Corbin with ex-secret service investigator David Caruso
So our thanks to Joe from Philadelphia, Martin in Edinburgh, Gerd and Florian from Hamburg, Joel in Basel and Philippe in Paris - they all helped chart the extraordinary globe trotting schedule of the Prince so we could understand the role he played in getting the Fraud Office investigation halted.
"To the moon and back and three times round the earth every year" was the answer the Prince's biographer and friend, Bill Simpson, gave me when I asked how much mileage Bandar clocked up in the Airbus.
The plane is painted in the blue and white colours of Bandar's favourite American football team, the Dallas Cowboys and has two ace crews working round the clock - one British, one American - ex Air Force One.
There have been some great parties on board featuring presidents and kings: Bush - senior and junior, Mikhail Gorbachev, Nelson Mandela, Bill Clinton and a clutch of British prime ministers - they are all friends of Bandar's.
Although the Prince declined to be interviewed by Panorama, Bill Simpson gave us an insight into the man who is known as an international Mr Fixit extraordinaire.
Prince Bandar's plane was the venue for many parties
"Complex, an enigma, amazingly generous but Machiavellian too" was Simpson's take.
It was Bandar, now Saudi security adviser who lobbied Downing Street to get the SFO investigation halted. And so it was - on grounds of public interest citing the risk the Saudis might withdraw co-operation in the war on terror.
Bandar too used his legendary contacts book in Paris turning up at a crucial moment to see President Chirac.
It sent a powerful message to the British government that a French warplane might well replace BAE's Eurofighter in the next huge Saudi arms deal which hangs in the balance at the moment.
Whatever happens next, Prince Bandar will no doubt continue to have a big say.
Panorama will be broadcast on Monday 11 June 2007 2030 BST