Leading Arabic broadcaster Al Jazeera said it had received a copy of the tape from the group, which has claimed responsibility for some attacks and kidnappings in the past.
The group, whose name refers to Iraq's fight against British rule, has often released videos of attacks on US troops on the leading Arabic broadcaster.
Confirming Britain's biggest loss of life since the US-led invasion of Iraq, British Defence Secretary Geoff Hoon said nine Royal Air Force personnel and one soldier were "missing, believed killed" in Sunday's election day crash.