All of the portraits on http://parliament.uk are copyright to http://dods.co.uk/
It has always been in the back of my mind to approach them and ask about relicensing with a free license (long shot, but maybe...).
Currently the images are licensed as freely usable with a non-commercial clause, which is obviously a sticking point to just using them straight out.
editor@dods.co.uk is the contact.
(pretty everything else on parliament.uk is licensed under the open parliament license BTW http://www.parliament.uk/site-information/copyright/open-parliament-licence/ )
Tom