Try get_iplayer. It's a Linux command-line tool to download the stream directly from the provider's servers. Despite it's name, it can get content from ITV Player and 4od too.
Hah - that particular show isn't even available on the catchup player! Assumed it would be, as I watched it/screen grabbed it live on their player. Oh well, people will have to put up with the shitty watermarked version I already have. It was utter bollocks anyway.