I didn't regard the ATCO as having done anything 'wrong', they probably would have realised had I stayed on the frequency longer and had the other a/c taken off. As it was, safety was not compromised, as the context of the messages made it easy to identify the intended a/c (as they were taxing/holding etc.) and I was replying with my full callsign.
But there was the potential for me to appear to be pulling the ATCO up for being slow to realise that they needed to do something, and as the whole thing was a non-event, my interest was in just nudging the guy in a friendly manner. In my opinion having a 'standard' phrase to call on at such times tends to sanitise the exchange and prevent any hard feelings.
Thanks for the feedback. Should the same situation arise again, I'd probably take Bright-Ling's approach, as that covers the situation that I may have not heard the other callsign correctly and beleive there to be a conflict when there is not! (I can make mistakes too <img src="smile.gif" border="0"> )