I found this guide:
http://www.knoppmythwiki.org/index.php? ... MythConfig
Having read the wiki above I pressed ALT + TAB to get an XTERM pop-up window at the time when it appears to have crashed at 50%. (I think that there is supposed to be a prompt to press ALT + TAB; maybe this is just a bug on mine).
This prompted me with every channel on RadioTimesUK, so I selected all the free channels. I then ran mythfilldatabase which appeared to work successfully because all the selected channels are now shown in the Channel Editor on mythtv-setup.