What does it do for the reputation of the administration of justice, asked Lord Justice Moses, if it can be perverted by a threat?

A failure to bear that “essential principle” in mind led to yesterday’s damning indictment.

It also exposes the delicate relationship between ministers and government law officers, recently the subject of a government review.

The Attorney-General treads a fine line: as both a government minister who superintends the prosecuting authorities and a legal adviser to ministers, the job contains an inherent conflict.

Until recently successive attorneys have succeeded in keeping a rigorous distinction, ensuring prosecuting decisions free from political influence. The halting of the BAE investigation under Lord Goldsmith’s tenure fuelled pressure for change.

What went wrong? Ministers cannot order the Attorney-General to halt a prosecution – but the former Prime Minister came close to it. Tony Blair accepted that it was not a step to be taken lightly, but said there was a supervening “national interest” at stake.

The director of the SFO, Robert Wardle, came to a similar view – after hearing representations from the Saudi Ambassador.

Two key factors undermine the ultimate decision: the Prime Minister appears to have reacted to a blunt threat from the Saudis to “get rid” of the investigation or face an immediate cessation of relations on security and intelligence, with lives put at risk. Furthermore, the threat was made by an official allegedly complicit in the criminal conduct under investigation.

Secondly, the background to that threat was that the biggest export contract for a decade, the Typhoon, was in the offing - and at risk of being lost to the French. So commercial considerations, while played down, were acutely in the frame.

The Saudis had increasingly become a significant partner in the intelligence war against al-Qaeda, providing crucial tip-offs of suspects, tracking their movements and letting MI6 know of any information that pointed towards a British connection.

However, did this cooperation with Riyadh justify Mr Blair’s claim that Britain’s national security was at stake? There were lurid tales of how the Saudis had warned London that if the SFO went ahead with its plans to investigate their secret bank accounts in Geneva, the intelligence flow would stop.

There is no question that if the intelligence partnership had ended this would have damaged Britain’s national interests. But, however many times it was denied, the principal reason for calling off the SFO dogs was to safeguard aircraft sales to the Royal Saudi Air Force, and the thousands of British jobs that went with it.

Ironically, the recent review of the Attorney-General’s role has largely endorsed the status quo. More than that, the Attorney’s power to direct that a prosecution be halted on security grounds will now be enshrined in statute.

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