Starring Amstell, Linda Bassett and Geoffrey Hutchings, the show's first episode averaged 1.56m (7.6%) on BBC Two between 10pm and 10.30pm.
An edition of Who Do You Think You Are? starring gardener Monty Don was watched by 5.4m (22.3%) on BBC One from 9pm.
The programme comfortably beat Identity in the 9pm hour, after the crime drama pulled in just 3.28m (13.5%) on ITV1 and 147k (0.6%) on ITV1 HD.
On BBC One, Cowboy Trap took 2.99m (14.3%) between 7.30pm and 8pm, before Panorama averaged 3.54m (15.2%) from 8.30pm. Later on the channel, factual series Gears And Tears grabbed 1.58m (10.4%) between 10.45pm and 11.15pm.
The second part of documentary mini-series Our Drugs War appealed to 780k (3.4%) on Channel 4 in the 8pm hour and 137k (0.6%) on Channel 4 +1. The programme was followed by The Hospital, which took 1.73m (7.2%) and 188k (1%) on timeshift.
Big Brother was watched by 2.26m (12.6%) on Channel 4 between 10pm and 11.10pm, and 151k (1.6%) on Channel 4 +1.
Wainwright's Walks: Coast To Coast averaged 1.17m (6%) from 7pm, before Roger And Val Have Just Got In took 980k (4.7%).
University Challenge and Antiques Master secured respective audiences of 2.52m (11%) and 1.85m (8%) on BBC Two in the 8pm hour. Dragons' Den pulled in 2.78m (11.5%) for the channel from 9pm.
Cricket On Five attracted 635k (3.1%) to Five between 7.15pm and 8pm hour. It was followed by the return of The Gadget Show, which averaged 1.28m (5.6%), up 230k week-on-week.
A screening of action film Collateral Damage appealed to 1.58m (7.6%) on Five between 9pm and 11.15pm.
Overall, BBC One narrowly won primetime with 21.3% against ITV1's 21.2%. BBC Two came in third with 8.6%, followed by Channel 4 with 6.3% (+1: 0.7%) and Five with 5.7%.
Elsewhere, a new episode of Britain's Next Top Model was watched by 242k (1%) on Living in the 9pm hour, down 81k week-on-week.
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BARB ratings data supplied by Attentional