The version on iPlayer is only a 30 minute extract and is only available until 12:59am Monday 3rd November, unless you download it, in which case you can keep it for 30 days.

Not sure how long the Electric Proms site will be there, but that version is 1 hour 38 minutes. Don't seem to be able to download it, but I guess you could capture the sound using Audacity or similar.