It's amazing to me that we even have to discuss this. A whole bunch of people were doing their best to do their best and it didn't work out. That's defined as the "fog of war". It's what warriors experience every time they strap on an airplane, a submarine, a tank or a ruck sack. There still isn't a perfect war machine that might prevent this.
My deepest sympathies go out to the family of the fallen British warrior. But just like Cindy Shehan's son, Casey, (who, unless I miss my guess, is rolling over in his grave) that young man would not want his family to persue all of this. I can tell you for sure that I would NOT have wanted my parents to make an issue of a blue on blue accident. Most of us that have experienced direct combat understand how this works.