You can only record from the built in Freeview, not from any other source such as the plugged in Virgin box.
Out of interest, why would you want to? The Virgin box can record 3 things at once. If you record using the USB, you cannot take that recording away to watch elsewhere. It can only be watched on the original TV.
Thanks for your reply and I have no reason to doubt what you are saying but in the accompanying manual there is no reference to recording exclusively from Freeview, it simply says a 'Digital Broadcast' is necessary. Why would Sony omit to say that you cannot record to USB if you have digital cable or a Sky STB (both are connected via HDMI).
I would want to because I have a cable HD box and not a Tivo. Tivo allows you to record, a cable box doesn't.
I bought the TV on the strength of the adverting blurb, which says 'record to USB from a digital broadcast'. This is obviously far from the truth. Why don't Sony make things clearer?