In sending my last reply, I had another dig around and seem to have found a solution which works. I went to the stereo pan and moved the line wholly to the top. For reasons I don't understand, that seemed to make a mono recording of both legs of the stereo output, which sounds fine, as opposed to the normal way of changing it to mono which always just picked up the worse leg.
Thanks very much for your help. I would not have found the answer without it.