We don't normally hear of missiles just "falling of aircraft" by accident and so it sounds like deliberate. What we don't know is the type of missile involved, radar guided or heat-seeking, and we also don't know if the Russianicon aircraft were targeting their radar at the Rivet aircraft.

I don't think that we can do anything if the Russians fire a missile in close proximity to one of our aircraft if they are not targeting it, i.e. the missile is fired so that it does not hit our aircraft.

I never really understood the logic of buying the Joint Rivet Aircraft for the RAF based on old airframes, older than the Nimrod R1's they replaced.