Install U-Torrent, and then go to this page and click on "Download this torrent", under the big green button.
Sit back and it will arrive, bit by bit, until it's all done. About 1.3Gb, so will take a while. You can then play it on your PC, or perhaps your TV if you have HDMI leads and ports. The file is not DRM protected, unlike the BBCI-player, so you can keep it for posterity.
I just wanted to thank airborne_artist for this link which was very successful. Does anyone know if there is a similar place where I can view the Ewan McGregor documentary that aired last Sunday night on the BBC?
I understand why they block non-uk viewers from watching these programmes on the interwebs, but I wish they'd offer some kind of subscription service to overseas viewers.