The ITV1 drama was beaten by ITV2's Britain's Got Talent spinoff, which averaged 1.66m (7.5%) over the same period.
The Prisoner - now in its third week of six - lost a staggering 85% of the lead-in audience from Britain's Got Talent, seen by 10.17m (43.4%) in the 8pm hour.
Earlier on ITV1, You've Been Framed! A To Z and The Whole 19 Yards averaged 3.4m (18.6%) and 4.04m (19.6%).
The fifth episode of Doctor Who, 'Flesh and Stone', pulled in 6.53m (32.8%) to BBC One from 6.25pm, on par with last week.
The latest edition of Over The Rainbow followed with 5.02m (23.9%), then The National Lottery: Who Dares Wins had 3.93m (16.7%) from 8.10pm. Casualty took 6.05m (27.2%) between 9pm and 9.50pm.
BBC Two's live snooker coverage averaged 1.77m (8.4%) for around four hours from 7pm.
Channel 4's repeat of documentary SAS: The Real Story appealed to 895k (3.8%) in the 8pm hour, then a screening of Jason Statham actioner The Transporter picked up 1.53m (7.4%).
On Five, NCIS, CSI: NY and Law & Order delivered respective audiences of 1.06m (4.5%), 1.79m (8%) and 1.15m (6%). A repeat of CSI closed out the night with 764k (5.9%).
BBC One claimed a primetime victory with an overall share of 23.1% to ITV1's 20.3%. BBC Two was third with 8.3%, followed by Five with 6% and Channel 4 with 5.3% (+1: 0.6%).
BARB ratings data supplied by Attentional