It's actually against the BBC's production guidelines to filmise HD productions- if you want a film look, then you shoot native 25p. Presumably the producers wanted a video look, but someone somewhere down the line decided to stick a film look on it- but they can only do it on the SD version, for the reason I mentioned above.
Another thing is all the people calling it "crap" and "not funny" have clearly missed the intentions of the show- it was a drama with a few laughs in it, not a sitcom. I watched it knowing this, and I enjoyed it a lot. People who hated it need to rewatch it realising this, you might enjoy it more.