it would be nice if aircraft fitted with Transponders turned them on, even where there is no radar coverage in class G!!
Could I just say that... it is MANDATORY that you turn your transponder on, if you have one, in ALL airspace. AIP ENR 1.1 section 71.1 refers. I suggest that a less-polite response be given if the TCAS target suddenly appears after asking them to turn it on.