The general rules is as follows:
b) In actual or simulated instrument conditions, only the pilot manipulating the controls or providing input to the auto-pilot may log all flight time as instrument flight;
However this comes from a document that has no legal standing, so that is why ATO's are suggesting otherwise. It would make for an interesting court case if someone tried to legally test your IF experience in court. (say you crashed an aircraft and they wanted to suggest you had been logging IF illegally and therefore didn't met the insurance minimums for the flight or something)