It's amazing how different the situation is wrt to OTA converter boxes this side of the pond :http://www.amazon.co.uk/s/ref=nb_sb_...x=freeview+box
Just a quick search on "Freeview box" on amazon.co.uk lists loads. These are mainly SD receivers though, so don't have to downconvert HD signals.
They're not quite the same as the US boxes, as most don't include RF modulators, as sets without AV inputs are incredibly rare in Europe where SCART has been knocking around since the early 80s.
In fact the smaller receivers are basically boxes with SCART plugs integrated into them that plug into the back of your TV (though SCART is a lousy connector mechanically and I bet they fall out). Some include basic recording/replay to/from USB external storage these days.
Freeview HD boxes, which will receive the HD channels in HD and output via HDMI (and usually also output an SD SCART or RCA composite output) are dropping in price as well They're going for sub £40 in supermarkets, with a Grundig model for £38 on amazon.