Starring Anna Friel and Daniel Mays, the first instalment aired on Wednesday after it was replaced in the channel's Tuesday night lineup.
Meanwhile, Celebrity Mastermind quizzed 5.1m (21.8%) from 7pm and Fake Britain was caught by 5.02m (21.6%) from 7.30pm.
Countryfile attracted 4.14m (16.7%) in the 8pm hour, with a midweek Match of the Day scoring 2.89m (22.5%) late from 10.45pm.
ITV1's programming was dominated by an airing of the movie Mamma Mia! from 8pm, which entertained 4.62m (18.2%) and a further 357k (1.6%) on +1. Harry Hill's TV Burp preceded it with 4.43m (18.9%).
BBC Two's lineup consisted of Hairy Bikers' Best of British (2m/8.6%), Nature's Weirdest Events (3.02m/12.2%), King George and Queen Mary: The Royals Who Rescued the Monarchy (3.13m/12%) and Mock the Week (1.44m/6.9%).
Over on Channel 4, How to Cook Like Heston served 1.51m (6.2%) from 8pm (+1: 223k/0.9%), The Fabulous Baker Brothers grabbed 1.69m (6.7%) from 8.30pm (+1: 172k/0.7%) and One Born Every Minute had 2.83m (10.8%) from 9pm (+1: 468k/2.5%).
The Bank Job earned 1.21m (6.5%) from 10pm (+1: 150k/1.4%).
Channel 5's Charley Boorman's Extreme Brothers took 375k (1.6%) from 7pm, The True Story drew 764k (3.1%) from 8pm and the film Beowulf averaged 833k (3.8%) from 9pm.
Overall, BBC One finished primetime with 19.2%, edging out ITV1 on 18.6% (+1: 1%). BBC Two (9.9%), Channel 4 (6.9%, +1: 1%) and Channel 5 (3%) followed.
On the multichannels, Pixar's WALL-E attracted 585k (2.4%) on BBC Three from 7.30pm.
BARB ratings data supplied by Attentional