The Daily Telegraph reports that:

The Army now believes that the Lynx helicopter shot down over central Basra at the weekend was most probably hit by a surface-to-air missile, obtained possibly from neighbouring Iran, after missile casings were discovered on the third floor of a nearby building, security sources in the city said yesterday.
The discovery, if confirmed, will be a worrying development for British operations in Iraq, which are increasingly reliant on helicopter “air bridges” to move men and equipment to reduce the risk of convoys being ambushed by roadside bombs.

If that missile can be traced back to Iran then it can be regarded as an act of war by Iran against the coalition. Rather than fretting about it, the coalition should launch a few missiles of it’s own against Iranian military facilities.