The Panorama report, in which reporter Tom Heap and his team found children in India sewing sequins onto Primark clothes, got the biggest audience in the 9pm-10pm slot with a 19.2% share.
Footage was shown of some of India's poorest people working long hours on Primark clothes in slum workshops and refugee camps, far away from the Primark-approved and inspected factories, breaking promises on child labour, working hours and wages.
When presented with the results, Primark sacked three of its suppliers.
ITV also put in a strong performance with its documentary 'Identical Triplets: Their Secret World' drawing in 4m viewers and an 18.4% share of the audience between 9pm and 10pm.
The programme explored whether four sets of triplets, including the UK's oldest surviving identical triplets, share a sixth sense that allows them to communicate between themselves.
The third part of BBC Two's 'Mary Queen of Shops' series attracted 2.5m viewers and an 11.1% share of the 9pm audience, beating the final part of Five's documentary series 'Warship', which pulled in 1.4m and a 6.4% share.
The final documentary in Channel 4's Victorian Passions season, called 'Upstairs Downstairs Love', netted 1.3m viewers and a 6% share of the audience between 9pm and 10pm. Including Channel 4+1 figures, it managed 1.4m viewers and a 6.4% share.
Channel 4's 'Big Brother' pulled in just 2.7m viewers and a 15.7% share of the audience between 10pm and 11pm. Including Channel 4+1 figures the show managed 2.9m and a 16.4% share.