From The Scotsman (emphasis mine):

British commanders fear reaction to American aggression

REPORTS of an increasingly hard-line US policy towards Iran are starting to worry British generals and diplomats, who fear the 9,650-strong UK garrison in southern Iraq would be targeted by Tehran in retaliation to any strike by the Bush administration....

Last summer’s capture of eight Royal Marines by Iranian Revolutionary Guards off southern Iraq has convinced many senior British officers and diplomats that any increase in tension with Iran would result in ‘blow back’ against British forces in Iraq. The marines were eventually released unharmed but it later emerged that Iranian gunboats entered Iraqi territorial waters to abduct the marines’ patrol boats....

There were credible reports that last summer Tehran concentrated troops along the border with Iraq in response to US sabre-rattling over the nuclear issue, raising the possibility that Iran might try to seize Iraqi territory.

Yikes.