The Office UK was shot in 16:9 576/50i SD, which was flickered to 576/25p in post.
Extras was mainly shot in 16:9 576/50i SD, again flickered to 576/25p in post. Some sequences were shot on film (I think - the excerpts from the film) and the series 2 sitcom sequences were left as 576/50i to give it that "UK sitcom" feel (most UK sitcoms are shot on video)
So - no they weren't shot in HD - but they were shot in 16:9 SD.
In the UK they were shown in 14:9 letterbox on 4:3 SD outlets, and 16:9 full-screen on 16:9 SD outlets. I guess in the US they were letterboxed on 4:3 SD outlets - but weren't upconverted to 16:9 HD on the HD outlets.