The programme, which documented life in the famous British prison, was watched by 4.98m (21.7%) on ITV1 in the 9pm hour.
Earlier on the channel, Countrywise pulled in 3.46m (15.4%) from 8pm to 8.30pm.
On BBC One, Panorama gained 2.05m (8.9%) from 8.30pm to 9pm. It was followed by retail reality series High Street Dreams, which appealed to just 2.18m (9.5%), a drop of 290k week-on-week.
Springwatch: Signs of Change With Chris Packham averaged 1.99m (8.7%) for BBC Two in the 8pm hour and was followed by 80-minute drama Royal Wedding with 1.65m (7.4%).
The Gadget Show saw a 150k week-on-week increase in its audience to 1.12m (5.3%) on Five in the 8pm hour, then FlashForward put in 1.56m (6.8%) from 9pm.
Later in the evening, Five's documentary about the formation of the Liberal Democrat/Conservative coalition government, titled Dave And Nick: Where Did It All Go Right?, appealed to 347k (2%) in the 10pm hour.
Nelson's Hospital: A Time Team Special gained 1.7m (7.4%) for Channel 4 from 9pm, and 93k (1.1%) on timeshift.
However, the second episode of Derren Brown Investigates suffered an 840k week-on-week drop to 1.36m (8.3%) on Channel 4 in the 10pm hour, with 161k (0.9%) watching on timeshift.
Overall, ITV1 dominated primetime with 25.2% compared to BBC One's 17.7%. BBC Two came in third with 7.3%, followed by Channel 4 with 5.5% (+1 0.6%) and Five with 3.9%.
Elsewhere, the latest episode of Glee attracted an impressive 1.26m (5.5%) to E4 from 9pm and 275k (1.6%) on timeshift.
BARB ratings data supplied by Attentional