Aerial only isn't normally supported (see the FAQ). If at all possible get a Freeview box and use that (or Satellite). If that is impossible it might be possible to add you to the limited list of special cases of aerial only support.
Edit: - from the FAQ
Q: Which programme sources are supported?
A: You can use Sky, Freesat, Freeview, Virgin Media or TalkTalk cable.
During Guided Setup you can select the following:
For ---> Freeview, Virgin Media orTalkTalk --- select ---> Aerial + Digital Cable/Digital Terrestrial
For ---> Freesat, Sky or Sky HD --- select ---> Aerial + Digital Satellite
For ---> Freesat, Sky or Sky HD + Freeview, Virgin Media or TalkTalk --- select ---> Digital Satellite + Digital Cable/Digital Terrestrial
There is only limited support for analogue-only source - i.e. "old style" terrestrial television. This will be phased out nearly everywhere by April 2012 so you should be looking to switch to Freeview or Freesat. For those people who cannot yet get Freeview and are unable to install a satellite dish (e.g. you have a listed building), a limited number of analogue-only lineups are available.
See this thread
viewtopic.php?f=8&t=546