According to Iraqi Captian Karim Asab, a roadside bomb exploded shortly before 10am (0600GMT) as a British military convoy was driving on the main road near Kahla.
"We confirm a hostile action against British forces ... which resulted in a fatality. The incident is now under investigation," a British military spokesman said from the southern city of Basra, where British forces in Iraq are based.
"There will be no further details until the next of kin have
Sky TV earlier reported that a roadside bomb had struck a British convoy in Amara, where British troops have frequently clashed with Shia militia.