Broadcaster ITV revealed it lost £50 million in annual advertising revenues after millions of viewers deserted its flagship channel.
Details of the sales fall emerged days after regulator Ofcom said ITV1 - home to Coronation Street and The X Factor - experienced a 3.6 per cent decline in its share of viewers in homes with access to digital or satellite services during 2005.
It was more than any other broadcaster.
ITV has looked to offset the decline by introducing new channels and revenue streams, including through the addition of website Friends Reunited.
The moves enabled total revenues to climb six per cent to £2.18 billion, while pretax profits rose 36 per cent to £452 million.
The UK's leading commercial channel said advertising revenues for ITV1 were down to £1.46 billion in 2005 and that its ad figure across the business was likely to be ten per cent off in the first quarter.
It blamed strong comparisons with a year earlier and the presence of Easter and the World Cup in the second quarter, although it is also facing tough trading conditions.
The group was boosted with the announcement that Uni-lever - maker of Dove, Lynx and Flora - had signed a four-year deal to buy £200 million of airtime across its channels running to the end of 2009.
ITV, which was formed by the merger of Carlton and Granada in 2004, has been battling to retain viewers and its share of the advertising spending pot as digital channels mushroom and the nation prepares for the analogue signal to be switched off.
Nobody was available to comment on the performance of Birmingham-based ITV Central.
The reach of so-called "multi-channel" television jumped to 60.1 per cent in December with audience share growing to 30.8 per cent while terrestrial channels lose viewers year-on-year, Ofcom said.
By the end of last September, 66 per cent of households (16.5 million) could access digital television.
ITV posted a rise in profits as the decline in advertising revenues at its terrestrial channel was offset with the growth at digital channels ITV2 and ITV3 which pushed total ad revenues up 2.7 per cent for the year.
The group said the decline in viewing figures for ITV1 was inevitable as people moved to greater channel choice on digital television.
ITV's share of viewers in multi-channel homes across all its channels grew seven per cent to 32 per cent, it said.
Last year, Ofcom slashed the costs of ITV's licences £135 million to help it cope with the challenges posed by the digital age.
The group's acquisition of the Friends Reunited website, in December, has seen a payoff with revenues up 75 per cent in January compared with a year ago.
Charles Allen, chief executive of ITV, said the group had moved from "an analogue, single channel federation to a multi-channel, multi-platform, content-driven business focused on the needs of viewers and advertisers".
ITV also announced the launch of ITV Play, a new "participation TV" digital channel, which will broadcast from April 19 on Freeview and overnight on ITV1 and ITV2 from March 31.
This follows the success of existing call-TV formats Quizmania and Play Sudoko, broadcast on ITV1 and ITV2 overnight in the last three months, the firm said.
Analysts remained positive after ITV said £300 million would be returned to shareholders and the dividend was lifted by 1.8p per share.
The deal with Unilever is predominantly for "spot" advertising breaks on ITV channels 1 to 4 and Men & Motors.
Nigel Cowlin, Unilever's head of media and communication in the UK and Ireland, said: "ITV is unique in its ability to deliver mass audiences in an increasingly fragmented market."
