Black Hole
May contain traces of nut
...the interface itself is a separate piece of software that they don't control ... I believe it's interpreted too but I don't know what language it's written in.
Just guessing - it may be a special purpose tokenised language for a virtual machine implemented according to specification, within the Humax code. This would make it easy to run the user interface on anybody's implementation of the VM. The DVD specification does something similar for the menu navigation - the code on the DVD runs in a VM implemented by the manufacturer of the DVD player.