Now that we can only get 1280x720 downloads at 50fps I wondered if it might be possible to convert to 25fps to ease storage requirements. I ran a file through Handbrake and it seems to have done the trick. Can any ffmpeg expert tell me the command to do the same thing?

Try:

As described in:
https://ffmpeg.org/ffmpeg.html#Description

Thanks, easy when you know how :) I just tried it on a 5 minute clip and it reduced the size from 171 MB to 57 MB, more than I would expect from just dropping every other frame. The bitrate went from 4368kbps to 1353 kbps.
I'll try adding it to a get_iplayer command now.

You may want to adjust encoding parameters to suit. Start here:

https://trac.ffmpeg.org/wiki/Encode/H.264