Anyone who happens to be reading this
I’ve solved (I think) my own problem. When I load Premier Pro it comes up with sequence 01 in the files panel and the timeline is also sequence 01. This was causing the problem. I couldn’t change the settings (still can’t) and it was creating a high res video which was, of course, much smaller than the lower res input. The solution was to create a new sequence (sequence 02) and set it to DV 4:3 aspect ratio. Then edit the raw footage in THAT sequence rather than sequence 01.
Paul