Hmmm, on further investigation, parliament.uk's images are not its own - their copyright page states

"All photographs of individual MPs and Peers on the biographical pages and Committee pages are the exclusive property of Dods and are protected under international copyright laws. The photographs may not be reproduced, copied, stored or manipulated in any form without the written permission of Dods unless for non-commercial purposes, provided permission is sought beforehand and the photo is credited. For more information on these photos, please email editor@dods.co.uk "