The latest instalment, which aired in its usual 9pm slot, pulled in just 1.84m (7.7%). The previous low for the second season came during episode three, which logged 2.11m (8.6%) on Friday, March 5.
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Earlier on Five, 781k (3.2%) tuned in for Highland Emergency.
Mastermind and Gardeners' World took 1.84m (7.8%) and 1.63m (6.6%) for BBC Two during the 8pm hour, then 2.01m (8.4%) watched Matsercrafts at 9pm.
Over on ITV1, Dancing On Ice Friday claimed 3.43m (14.5%) between 8pm and 8.30pm, then Michael Winner's Dining Stars had 1.92m (8%) during the 9pm hour.
A Place In The Sun and Embarrassing Bodies took 1.14m (4.7%) and 1.91m (7.9%) for Channel 4 at 8pm and 9pm respectively.
BBC One's coverage of Sport Relief 2010 averaged 7.84m (33.2%) between 7pm and 10pm.
Overall, BBC One dominated primetime with an average share of 31.3% to ITV1's 17.5%. BBC Two was third with 9.9%, followed by Channel 4 with 4.9% (+1: 0.7%) and Five's 4.2%.
Over on the multichannel stations, the latest episode of Lost managed 509k (2.1%) for Sky1.
BARB ratings data supplied by Attentional