I also received a reply from freesat (all my emails to them returned as out of office, hence my finding this forum and posting here). Anyway for anyone else their answer agrees with Gonzo, but also mentions that the route I took to On Demand does work,but only partially; Response posted here:
Thank you for your question in regards to not receiving access to the full range of great On Demand content.
Currently we do not display On Demand content such as 4OD, Youtube, Demand 5 via the TV listings guide, this is due to only two services (BBC iPlayer and ITV Player) being available across all our boxes via our TV listings.
The rest of the great On Demand services are available by the On Demand menu which is accessible by pressing the home button on your Humax remote located up and left of your OK button, then scroll up to On Demand and press OK, this should then list the full On Demand content we offer.
SO glad I found this forum