Channel 4 suffers 2013 ratings slump
Channel 4's overall share of viewing has fallen 11.4% over the past year, figures show.
The broadcaster's share fell from 6.5% to 5.8%, according to industry paper Broadcast, in part due to bumper Paralympics audiences last year.
ITV scored the channel's first share increase in 23 years from 15.7% to 16.5% including its timeshift services.
BBC One suffered a slight drop from 21.3% to 21.1%, but it remains the UK's most popular channel.
Although Channel 4 has screened ratings hits including US terrorism drama Homeland and Southcliffe, other shows such as Bedtime Live and One Born Every Minute struggled.
BBC One's decision to scrap children's content from afternoons also contributed to Channel 4's decline.
A spokesman for the broadcaster told Broadcast: "There are easier ways to maximise audience share, but Channel 4 has a remit to take creative risks, champion alternative voices and stimulate debate.
"We have done this across 2013 with programming that has also achieved audience success - from The King In The Car Park, Utopia and Murder Trial to Southcliffe, The Mill and Educating Yorkshire."
The channel also stressed that 28 of its top 50 shows were new titles.
ITV was the only one of the five main channels to increase its audience share, after a steady decline in recent years as well as a big slump in 2012 as viewers switched to the BBC to watch the Olympics and the Queen's Diamond Jubilee.
However, ratings winners I'm A Celebrity...Get Me Out Of Here! - whose launch show was the most-watched programme of the year so far - Britain's Got Talent, Downton Abbey and Broadchurch helped secure an improved performance.
"We needed to bounce back and we have," Peter Fincham, ITV director of television, said.
"We're coming good on drama, we've got good entertainment and more new entertainment shows that will return."
ITV also benefitted from BBC Two replacing original programming in its afternoon schedule with repeats of old shows as part of its cost-cutting plans, resulting in its share falling from 6.1% to 5.7%.
BBC controller Janice Hadlow said the channel had performed "exceptionally well" despite its "loss of daytime origination".
She pointed to ratings successes including James Corden's comedy The Wrong Mans - which gave the channel its biggest comedy launch in more than eight years - Horizon: The Secret Life of the Cat and Gillian Anderson drama The Fall.
With BBC One's largest audience share for five years in 2012 due to the Olympics, it had been expected ratings would likely fall this year, but other notable events and stable ratings winners such as Strictly Come Dancing and Mrs Brown's Boys helped its performance.
"BBC One is the nation's favourite channel, bringing audiences together for the big events including Andy Murray's Wimbledon victory and the Doctor Who 50th Anniversary which topped the charts as the highest rating drama of the year across all channels," a BBC spokesman said.
Channel 5's ratings remained fairly stable, with its share marginally down 0.4% to 4.5%.
Ben Frow, director of programmes, said the channel was "in a very good place".
"We've worked hard this year and it's paying off. Programmes like On Benefits and Proud show that we can be populist and smart and at the same time unexpected, with something like The Bible," he said.
Sky One was the top digital station, increasing its share to 1%.