Thank you Luke, you've got me right, that's exactly what I needed. I was hoping to say BRILLIANT, but it does not seem to have worked.
First I installed the upgraded webif package 1.4.8-8. This gave me many more packages and I was able to install opkg-beta. I then found the iplhack package and installed that.
I then set the Humax on standby with the remote, waited for silence + 15 seconds or so, and re started. Then I remembered BH's instruction so I also rebooted the Humax from the Diagnostics screen.
Turned on the telly, hit the TV Portal button, selected I-Player and tried to run a program. After ~30 seconds I got the "Something went wrong loading the programme." screen. Hit OK and it brought up the programme screen to run again but still produced the "went wrong" screen.
I look on my Package Management screen and iplhack is installed but I cannot any longer see opkg-beta anywhere at all.
EDIT: I now see that there is an upgrade of webif available to 1.4.8-11
Should I install this??