The third part of the mini-series, which stars James Nesbitt and Minnie Driver, averaged 3.77m (16.4%) for BBC One in the 9pm hour, down 740k week-on-week and 1.2m on its debut broadcast. Meanwhile, a further 228k (1%) watched the new episode on BBC HD.
Despite its ratings dip, The Deep was still able to beat The Bill in the 9pm hour, after the police drama grabbed 3.2m (13.9%) for ITV1, with an additional 112k (0.5%) tuning in on ITV1 HD. Earlier on ITV1, Grimefighters secured 2.27m (11.7%) from 7.30pm.
New Who Wants To Be A Millionaire? appealed to 3.31m (14.7%) on ITV1 in the 8pm hour, but the gameshow was outperformed by Holby City, which took 5.48m (24.4%) on BBC One.
After their successful debut yesterday, Jason Mountford and Alex Jones continued to attract viewers to The One Show, with 4.5m (24%) watching from 7pm.
Coast appealed to 1.64m (8.3%) for BBC Two in the 7pm hour, before new factual entertainment series The Great British Bake Off took 2.03m (9.1%). Later in the 9pm hour, That Mitchell And Webb Look and Shooting Stars secured respective audiences of 1.45m (6.3%) and 1.58m (6.8%), then Russell Howard's Good News grabbed 1.18m (5.8%).
Sarah Beeny's new property series Help! My House Is Falling Down averaged 2.12m (9.5%) for Channel 4 in the 8pm hour, with an impressive 381k (1.7%) watching on timeshift. Who Knows Best: Fighting The Fat took 1.65m (7.1%) in the 9pm hour and 207k (1.1%) on timeshift. It was followed by Big Brother, which pulled in 2.24m (12.9%) from 10pm.
Over on Five, Chris Barrie's Massive Speed brought in 336k (1.6%) in the 7pm hour, before Great Railway Adventures took 931k (4.2%). CSI: Miami and CSI: New York grabbed respective audiences of 2.12m (9.2%) and 1.42m (7.6%) for the channel from 9pm.
Overall, BBC One dominated primetime with 22.5% against ITV1's 14.7%. Channel 4 came in third with 8.1% (+1: 0.9%), followed by BBC Two with 7.3% and Five with 5.6%.
Elsewhere, the return of Johnny Vegas's sitcom Ideal pulled in 658k (4.1%) for BBC Three between 10.30pm and 11pm.
> Soaps Ratings Roundup: August 11
BARB ratings data supplied by Attentional