The C4 series, which sent successful property investor Caroline Marsh and two-year-old son Ashley to the deprived area of Toxteth, Liverpool, trumped BBC One's comedy drama 'Mutual Friends' for the second week in a row. 'Mutual Friends' pulled in 3.2m viewers for a 14.5% audience share.
'The Secret Millionaire' returned to the top of the ratings pile once more after falling behind ITV1's Uefa Champions League match between Liverpool and Marseilles last week.
The series has proved more popular this time around, with average live and 'viewing on same day as live' (Vosdal) ratings per episode of 4m, up 38% on the previous series.
The final instalment of the series was followed by wrap-up show 'Secret Millionaire Changed My Life' in the 10pm slot, which drew an additional 2.5m viewers for C4.
Channel 4+1 brought in an extra 195,600 viewers for 'The Secret Millionaire' and 134,100 for 'Secret Millionaire Changed My Life'.
ITV1's documentary 'Leslie Ash: Face to Face' aired last night, and followed the former 'Men Behaving Badly' star as she examined the pressure placed on actresses to stay young-looking, including wince-inducing footage of botched plastic surgery jobs. 'Face to Face' drew 2.7m viewers for a 12.7% audience share.
On Five Horatio Caine unravelled the case of a tourist shot dead in 'CSI: Miami' with 2.4m viewers and an 11.3% share.
Welsh comedian Griff Rhys Jones examined the roots of anger and why men, in particular, so often lose their temper. The first of the two-part documentary on BBC Two drew 1.3m and a 6.3% share.