Last night's episode, starring Dennis Waterman and Amanda Redman, featured a light-hearted plot about a man who died by falling into a vat of real ale.
It netted a 35.6% share of the 9pm-10pm audience to win the primetime slot for BBC One.
The third episode of BBC Two's 'Dragon's Den', featuring hopefuls pitching soft toys based on roadkill animals, eco computers and a high-wire adventure park, came in second with 3.4m viewers and a 14.6% share.
It beat the final part of ITV's 'Police, Camera, Action' documentary which attracted 3.1m and a 13% share.
Last night's fifth and final episode, called 'Car Tech Maniacs', saw Alastair Stewart taking a look at the in-car gadgets that distract drivers and the new tools the police are using to detect dangerous drivers.
The final part of Channel 4's 'Can't Read, Can't Write' documentary, following the journey of nine illiterate adults learning to read and write, drew 1.2m viewers and a 5% share of the 9pm-10pm audience.
Earlier in the evening, the first part of Channel 4's new documentary series 'The Genius of Charles Darwin' attracted 1.4m viewers and a 6.7% share of the 8pm-9pm audience. Including Channel 4+1 ratings it managed 1.5m and a 7% share.
Five's repeat of 'Greatest TV Comedy Moments', featuring Richard Wilson counting down the top 50 greatest comedy moments on TV, pulled in 943,000 viewers and a 4.8% share of the 9pm-11pm audience.
'Big Brother' attracted 3.1m viewers on Channel 4 and a 17.1% share of the 10pm-11pm audience. Including Channel 4+1 ratings it managed 3.2m and an 18% share.
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