Thanks Tom for responding to my call for assistance!
The HD and the mini DV clips were both filmed in 16:9. When I drop an HD clips into the timeline with the other 16:9 DV clips, it shrinks itself into the frame. I’ve also noticed that it appears as a much wider looking 16:9 than ‘normal’ 16:9. Up till now I’ve been managing the problem by zooming in on the clip so that it fills the entire frame, but this is not ideal.
I have also tried right clicking on it and selecting ‘remove attributes’ but all this does is make a very small adjustment in the width of the clip but does not solve the other distortions.
It also flicks outwards every time I put a title or subtitle over it, so it ends up zooming in and out on playback!!