Any move by the US Justice Department to pursue the bribery investigation into BAE Systems could aggravate frayed relations between America and Saudi Arabia.

Washington’s strategic alliance with Riyadh, built on the exchange of American muscle for Saudi oil, has been one of the most durable partnerships in the Middle East. It has survived several Arab-Israeli wars, conflicts in the Gulf, the oil crisis of the 1970s and the aftermath of the September 11 attacks, when 15 of the 19 terrorists were identified as Saudi citizens.

President Bush has worked hard to maintain the relationship with King Abdullah, but the chaos in the region has taken its toll. The Saudis have been frustrated by America’s failure to make any headway on the search for peace between Israelis and Palestinians. They are infuriated that a Shia Muslim Government has taken power in Baghdad, dislodging their traditional Sunni Muslim brethren. The Saudis also believe that Mr Bush is a lame duck and are concentrating their efforts on the next occupant of the White House. King Abdullah has also cast himself as a regional powerbroker at the expense of the Americans.

In February the Americans were speechless when the Saudis brokered a deal for a national unity government between the rival Palestinian factions Fatah and Hamas. Hamas, the radical Islamic group that pioneered the use of suicide bombers against Israel, gained instant respectability without having to recognise Israel or renounce violence.

King Abdullah compounded the insult in March when he opened an Arab League summit meeting in Riyadh by describing Iraq as under “an illegal foreign occupation”. More recently, he rebuffed the United States-backed Government in Baghdad when he refused to meet Nouri al-Maliki, the Iraqi Prime Minister.

“The Bush family has had a long relationship with Saudi Arabia, but that is coming to an end,” a US source with close connections to Saudi Arabia said. “The Saudis have concluded that Bush is finished and are not wasting any more time with him.”

Into this mix a new investigation into allegations that BAE Systems bribed Saudi officials in the al-Yamamah arms deal could drag the relationship to a new low. The leadership in Saudi Arabia values its privacy above all else. As the Serious Fraud Office discovered to its cost last year, when its own investigation was halted, the Saudis will use their leverage to block prying by outsiders.

But the US Justice Department will be difficult to deter. It is a far more powerful institution than its British counterpart, and Riyadh relies on US hardware for the bulk of its military needs. Crucially, Mr Bush may not be in the mood to grant Riyadh any favours in the present climate.

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