Ok so it appears I am totally lying…
Although the plugin illustrates that it is importing 9 images and is half way done, it has actually imported almost 600 images which suggests there are possibly 1200 images in total.
Even still I have left the computer on for 24 hours and it still stops at the same point.
I have just deleted all posts, comments and images. I then downloaded and installed the twenty twelve theme but it still behaves in the same way.
On re-import the plugin firstly downloaded 16 images, and then stopped. I restarted it and then it imported a total of 27 and then did the same again and totaled 52 images.