Speaking of BBC2, I've been surfing BARB...
BBC 2 Original Dramas 2011
Figures include HD where applicable and figures are available on BARB. (It'll be a damn sight easier when there's a BBC2 HD

)
(No. of episodes in brackets)
Eric and Ernie (1)
..6.65m
United (1)
....3.88m
The Sinking of the Laconia (2)
....3.49m
The Night Watch (1)
..3.20m*
The Shadow Line (7).
...2.45m
The Crimson Petal and the White (4)....2.06m
Christopher and his Kind (1)
...1.20m*
*Overnight figures
With a decent timeshift, The Night Watch should be up there with United and Laconia in the officials, behind only the huge Eric and Ernie.
Some pretty decent ratings in there, though one-offs or two-parters are evidently doing a lot better than the longer serials as retention appears a problem (regardless of critical acclaim). The Shadow Line fell from mid-3m on premiere to sub-2m by the end - and the Crimson Petal was down sharply too. All indications would point to a strong launch from The Hour next week, but we can probably expect it to fade somewhat going on this years trends. I hope not - the channel could do with a signature drama to get it recognised and everything I've heard about The Hour has been brilliantly positive so far.