The Saudi regime is under siege. To the west, its heaviest regional ally, the Egyptian dictator Hosni Mubarak, has been ousted. To its north, Syria and Jordan are gripped by a wave of protests which shows no sign of receding. On its southern border, unrest in Yemen and Oman rages on. And troops have been dispatched to Bahrain to salvage its influence over the tiny kingdom exerted through the Khalifa clan, and prevent the contagion from spreading to Saudi Arabia’s turbulent eastern provinces, the repository of both its biggest oil reserves and largest Shia population.