Channel 4 audiences have slipped to their lowest level in more than a decade as the station faces increasing competition from digital channels.
Figures compiled by the Broadcasters Audience Research Board (Barb) showed that the channel's audience share was 9.5 per cent over the past six months, down from 10 per cent last year.
The dip below the station's long-standing share of one viewer in 10 was partly caused by disappointing viewing figures for flagship shows including Boys and Girls, the ditched Saturday night entertainment show, and the Richard and Judy chat show.
Big Brother, which has been a mainstay of Channel 4 in recent years, has also struggled to interest viewers this summer in its fourth run.
Tim Gardam, who recently quit as director of television at the channel, admitted that the disastrous breakfast show RI:SE might never succeed.
Channel 4's digital station E4, with other multichannel services such as Sky One and ITV2, continued to grow.
Mark Thompson, Channel 4's chief executive, said in April that the station needed to return to its core creative values and be "Britain's bravest and most original broadcaster".
The latest figures show that all terrestrial channels are losing audiences as the number of multichannel homes increases.
Saturday night viewing figures for ITV1 are the lowest in a decade. Judgement Day, the new game show hosted by Brian Conley, has attracted only 3.3 million viewers, with The Vault, another game show fronted by Melanie Sykes, pulling in only 3 million.
ITV and BBC each had a 19.6 per cent share of viewers in multichannel homes.