There is no shortage of interested parties in the saga of the alleged £1 billion kickback who would like the public to think it too complex to be worth close examination. It is not. There are two straightforward explanations for how Prince Bandar bin Sultan comes to be accused of receiving £120 million a year for ten years via BAE in return for facilitating a deal to supply Saudi Arabia with Tornados and Hawk trainer jets.

In one, Prince Bandar receives the money as a normal commission, and as part of a deal to supply and operate the long-range Airbus that he requires as his country’s foremost international envoy. The Serious Fraud Office (SFO), which struggled to prove that a crime had taken place, then shuts down a criminal inquiry of the affair to protect national security. However, the other explanation is that successive British governments connive at covert personal payments of dubious legality and breathtaking size to secure the deal in the face of stiff foreign competition. Tony Blair then ends the investigation to protect Prince Bandar and BAE. The truth is that both explanations may be, in part, accurate.

It is pointless to pretend that the Middle Eastern arms trade is anything but murky, or that the Ministry of Defence can have been unaware of the alleged payments. Until Monday, these were claimed to be of the order of £60 million. New reports describe a scheme to pay £30 million, four times a year for ten years, into accounts set up for Prince Bandar. The sheer scale of such a scheme would make ministerial ignorance of it highly implausible, especially since, as BAE Systems noted yesterday, this was from the outset a “government-to-government” deal.

It is equally pointless to pretend, as the SFO has since the closure of its investigation last December, that no weight was given to commercial considerations in this decision. The bulk of the al-Yamamah deal may now be history, but maintenance contracts still keep hundreds of BAE Systems staff in Saudi Arabia, and the firm’s successor contract to supply 72 Eurofighter Typhoons is worth at least a further £6 billion. The deal’s fluctuating fortunes make a compelling timeline: on December 1 last year Dassault, the French firm, announced it was competing for the Typhoon contract. Two weeks later, Lord Goldsmith, the Attorney-General, declared the SFO investigation over. Three weeks after that, the Saudi Defence Ministry decided in favour of the Typhoon. The deal has not yet been signed, however and, after the latest wave of corruption allegations, Riyadh has signalled it may be delayed again.

The naming of any member of the Royal Family in an alleged corruption scandal is highly embarrassing for the Saudi Government. Yet the fact is that Prince Bandar’s high-level contacts have made him a vital conduit for intelligence-sharing on the Islamist terrorist threat for many years. It is precisely his role in the affair that gives credence to the official insistence that national security was at stake.

The case for a public inquiry or reopened investigation is weak. But the case for diligent enforcement of new anticorruption laws is strong. The BAE affair has made Britain look less like an anticorruption crusader than a hypocrite. In both London and Riyadh, greater transparency may cost deals in the short term, but its long-term dividend will far outweigh those losses.