Well, I've fiddled about with snooper again and looked at a few files and come up with this:
rtsp://3gp-acl.bbc.co.uk:554/radio4/secure_auth/mobile/RBN2_radio_4_fm_-_sunday_2130_b00t2rf2_2010_06_27_21_15_38.mp4
looks promising - doesn't it. But everything I have tried it in has rejected it one way or another I wonder if there are other bits of software to try.
It may be of course that it just won't work regardless of the software, but it does look like it might.
I've tried,
NetTransport,
Orbit Downloader, and free downloader. Any thoughts anyone.