In an interview granted to the Israeli television, George W. Bush warned that he was willing to resort to force against Iran to prevent it from getting the nuke. Once more, that war should count on British support. The justification could be that a U.S. – British attack would be the only way to mitigate the failure of the international community and that their action would be the only way to prevent Israel’s attack.
Common sense shows that the U.S., stuck in Iraq, cannot attack Iran. However, that would not be in tune with US objectives and resources. The devastating US air force power has not yet been rallied in Iraq and lots of troops are still likely to be mobilized to take over the coastal oil areas and launch raids against Iran. Bombing would target the political, military and economic (but oil) infrastructure of the country, and it would not restrict itself to those areas allegedly containing mass destruction weapons. On the other hand, Iran could also be the victim of a civil war as the US keeps pushing Azeri and Kurdish separatist movements.
The consequences of such an attack are not unknown: the development of terrorism, a Shiite uprising in Iraq, an attack by Iran and the Hezbollah on Israel, attacks against the Gulf oil industry, a price rise of the barrel and the world recession. However, since Iran is a threat to US supremacy and it essentially supply China with its oil– the other great opponent – the U.S. will accept those difficulties.
The U.K. will most probably participate in this war. As the existence of Iran’s nuclear program is a proved fact, it will be easier to persuade public opinion. Furthermore, the US will refuse to give the U.K. the substitute of the Trident submarine nuclear program if the British don’t pay for it with their own lives. Finally, the conservatives’ favorable vote should allow reducing defections in the Labor Party ranks. In order to stop this, we must support the strengthening of international treaties against all mass destruction weapons and free our intelligence service of the U.S. influence. To conclude, we must bring pressure to bear on our representatives.

Source
The Guardian (United Kingdom)

How Bush would gain from war with Iran”, by Dan Plesch, The Guardian, August 15, 2005.