At the moment this setting (on a UIImageView for instance) will keep the centre of the UIImage in the centre of the UIImageView and "crop" the edges that exceed the bounds equally on both sides.
Is there a way to change this at all?
For instance, if I wanted it to keep the top edge of the UIImage in line with the top edge of the UIImageView and just crop off the bottom when scaled etc...
One approach is to keep using UIImageView's automatic scaling (UIViewContentModeScaleAspectFit or UIViewContentModeScaleAspectFill, so that the aspect stays right), and then lop off the parts you don't want by applying a layer mask.
Alternatively (this is what I would do), just draw the image with the desired cropping, yourself.
For example, set the image as the contents of a layer and then set the layer's contentsRect (this determines what region of the image is displayed as the layer's contents) and contentsGravity (this determines how the image is pinned / scaled to the layer's bounds). You can change those values in real time (and it is even animated).
Or, when you want a cropped version, just whip out a new image graphics context, draw the image into it repositioned so that the right area overlaps the context in the right way, pull out the result image, and display it.