Hello,
I'm a journalist who also bought a UM7400, myself. I've been doing some digging for an article about this problem and wanted to share my findings:
1. Unfortunately there is no requirement for LG to support channels in MHEG format, only HBB.
2. Equally unfortunately, despite dropping this requirement, Freeview have NOT given broadcasters a deadline to migrate to HBB
3. The upshot is that LG aren't wrong, but given that the TV is physically capable of MHEG services (they work if you change the settings to Republic of Ireland and do a retune, but this causes EPG issues so it's not an ideal workaround), I am pushing LG for a firmware drop to fix the problem out of goodwill, given that there is no end-date for this situation.
4. I am also contacting ASA and OFCOM to see if, given the cost of a TV, they consider this an acceptable situation.
If I hear any more, I'll let you know. Not the news you probably wanted, but these are solid facts and that's still progress!