Starring Tom Hollander and Olivia Colman, the show's final episode averaged 1.69m (8%) on BBC Two between 10pm and 10.30pm.
An edition of Who Do You Think You Are? starring actress Dervla Kerwin was watched by 5.07m (21.3%) on BBC One from 9pm.
The programme comfortably beat Identity in the 9pm hour, after the crime drama pulled in just 3.44m (14.5%) on ITV1 and 138k (0.6%) on ITV1 HD.
Coronation Street performed best in the primetime soap ratings, with 8.54m (37.6%) watching the second transmission on ITV1 from 8.30pm. A further 221k (1%) tuned in on ITV1 HD.
On BBC One, Cowboy Trap took 3.38m (16.5%) between 7.30pm and 8pm, before Panorama averaged 2.83m (12.5%) from 8.30pm. Later on the channel, factual series Gears And Tears grabbed 1.77m (11.2%) between 10.45pm and 11.15pm.
New documentary mini-series Our Drugs War appealed to 910k (4%) on Channel 4 in the 8pm hour and 149k (0.6%) on Channel 4 +1. The programme was followed by The Hospital, which took 1.72m (7.2%) and 174k (0.9%) on timeshift.
Big Brother was watched by 2.19m (12.2%) on Channel 4 between 10pm and 11.10pm, and 204k (2.2%) on Channel 4 +1.
Wainwright's Walks: Coast To Coast averaged 1.04m (5.4%) from 7pm, before Mastermind: Champion Of Champions took 1.55m (7.5%).
University Challenge and Antiques Master secured respective audiences of 2.56m (11.3%) and 1.98m (8.8%) on BBC Two in the 8pm hour. Dragons' Den pulled in 2.92m (12.2%) for the channel from 9pm.
Extreme Fishing With Robson Green attracted 225k (1.1%) to Five in the 8pm hour and it was followed by the return of The Gadget Show, which averaged 1.05m (4.6%).
A screening of action thriller The Rookie appealed to 931k (4.6%) on Five between 9pm and 11.15pm.
Overall, ITV1 narrowly won primetime with 21.7% against BBC One's 21.1%. BBC Two came in third with 9.1%, followed by Channel 4 with 6.5% (+1: 0.7%) and Five with 3.6%.
Elsewhere, a new episode of Britain's Next Top Model was watched by 323k (1.4%) on Living in the 9pm hour, up 69k week-on-week.
A double-bill of comedy Benidorm took the second and third biggest multichannel ratings of the night, with respective audiences of 876k (3.7%) and 876k (3.6%) on ITV4 in the 10pm hour.
However, an episode of Family Guy secured the evening's largest multichannel audience, with 921k (9.9%) tuning in for the broadcast on BBC Three at 11.25pm.
BARB ratings data supplied by Attentional