trial and error while waiting for someone to deign to reply led to changing the file arrangement in finder. there the file is revealed not just as a wrapper but a .zip file. Unzipped you get AVCHDTN, BDMV and IISVPL. STREAM below BDMV lists the .mts files.
quite why it has to be so f**king obscure is beyond me. that'll teach me to want to do things a way that steve jobs hasn't prescribed I guess; and has wasted forty-odd quid of my money.
IMOVIE 9.09 BECAUSE THE LATER VERSION IS HOPELESS FOR THE WORK I DO.
None of which explains why 12 months ago the files showed in finder properly. after leaving the camera unused it now shows like this..