Had German officers been tried for war crimes committed against civilians in Germany at the request of the German government (the Nazis) and had they tried to use the "I was only obeying orders" excuse at Neuremberg, would it have been accepted because they committed their war crimes at the request of the government of the country in which the crimes were committed?

If not, then the excuse that British forces are there at the request of the Iraqi government shouldn't hold any water in any case in which someone refuses to commit what they understand (under international law) to be a war crime.