The show, which showcases "genius" ideas proposed by members of the public, beat the final episode of Channel 4 comedy Free Agents, which had 670k (3.6%) at the same time.
It also fared better than Al Murray's Multiple Personality Disorder, seen by just 1.27m (6.1%) on ITV1 at 9.30pm.
The most watched comedy on Friday night was Q.I., which brought in 4.67m (21.7%) for BBC One at 9pm. ITV1's Moving Wallpaper had 1.82m (8.5%) at the same time.
Lee Mack's Not Going Out took 3.59m (17.4%) for BBC One at 9.30pm.
The latest episode of Ramsay's Kitchen Nightmares USA delivered 2.56m (12.1%) for Channel 4 in the 9pm hour, with a further 423k (2.6%) on Channel 4+1.
Five's NCIS notched up 2.51m (11.8%) at the same time, while the final episode of BBC Two documentary Rocket Science took 1.29m (6.1%).
In the 8pm hour, Gardeners' World managed a decent 1.92m (8.5%) for BBC Two. Channel 4's A Place In The Sun: Home Or USA? was seen by 1.36m (6%), and on Five, Police Interceptors had 1.08m (4.8%).
BBC One came out on top in primetime overall with an average share of 21.8% to ITV1's 19.9%. Channel 4 was third with 6.4% (+1: 1%), followed by BBC Two with 7.3% and Five with 5.9%.
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Ratings data supplied by Attentional