Available in iPlayer but can't download

[Clive]

The following url plays in iplayer but I can't download it with either 
url or pid:

http://www.bbc.co.uk/iplayer/episode/p00lfrb3/Alistair_Cookes_America_The_First_Impact/

Both commands tell me what the program is, but neither will d/l and I've 
also tried a range of mode settings but both commands exit, telling me 
to try other modes. I generally have no problems with audio or video.

Is anyone able to enlighten me please?

Thank you.

Clive