I think you might have difficulty going back further.
Putting this in perspective the Americans have lsot 60 soldiers in Iraq just through general non combat accidents, road accidents etc. I don't know what the UK figures are but I'll bet the risk of a soldier being killed in friendly fire is of the same order as being killed in a road accident.
A little off track, but for the US troops during the Gulf War, friendly fire accounted for more than 23 percent of the Americans killed in action and 15 percent of the wounded.