BBC1 political thriller State of Play may have been trounced in its ratings battle with ITV1 last night, but it attracted a core of loyal followers - nearly 500,000 switched to BBC4 at 10pm for the second episode, giving the digital channel its biggest ever audience.
State of Play proved no match for ITV1's Caroline Quentin drama, Blue Murder, between 9pm and 10pm last night.
The BBC1 drama, which stars David Morrissey and John Simm as a highflying New Labour MP and an investigative journalist who get caught up in a political conspiracy following the murder of a parliamentary researcher, was watched by 5.2 million viewers according to unofficial overnights.
Blue Murder attracted 8.4 million over on ITV1, comprehensively winning the head to head battle with State of Play.
But at 10pm last night, BBC4 was the benefactor as nearly 500,000 State of Play viewers decided to stay glued to the box for the second episode and switched over from BBC1.
The second instalment of the show was watched by 480,000 viewers on BBC4 between 10pm and 11pm.
This was a whopping four times the previous audience high for the channel, which is believed to have been the 121,000 who tuned in to watch The Falklands Play in April last year.
BBC4 has been critically well received since launching in March 2002, but with its niche audience of arts and culture fans, it has inevitably struggled to attract decent sized audiences.
Even the most successful series, such as repeats of Horizon science documentaries and the Great Britons history show, have only averaged just over 30,000 viewers.
And many BBC4 shows have attracted audiences of under 10,000 viewers.