Well after speaking to my son (a very technical conversation considering he’s seven lol) turns out he couldn’t get the iPlayer working either so he watched a present recorded episode instead. However after a bit of investigation I found the iPlayer worked OK through the backwards EPG.
Reading up on the subject, I tried the update file humax offer for on demand issues, but that didn’t help. I then rolled back to an older firmware I had from the last time I did a manual update, and the problems remained.
I noticed the iPlayer seemed to have stored data in it which wasn’t being effected by the software updates (previous searches etc remained) so I did a factory reset to clear the data, and hooray the iPlayer works again.