Industry sales figures have shown that the network's December advertising revenues fell 3.7% year on year to £124.5m, while sales for January are £116m, a decline of 1.9% on last year.
Sales for February are also believed to be down, and forecasts show that it could fall by at least 5.2% to £113m. At this rate, the broadcaster's share of advertising could fall to below 50%. Analysts had forecast ad share of 51% this year, according to a report in the Sunday Telegraph.
ITV has been severely hit by the advertising downturn at a time when its publicly-funded rival the BBC has increased investment in the type of populist programming traditionally found on commercial channels.
Last week it was reported that BBC One had widened its narrow lead over ITV1 in all-time viewing by 2.1% on last year. BBC One averaged a 26.1% audience share for the year compared with 24% for ITV, according to unofficial overnights reported in Marketing.
ITV is also suffering from increased competition from Five, formerly Channel 5, and multichannel offerings.
The network has reacted by upping its programming spend by £100m this year and by commissioning a number of big budget dramas including last year's remake of Dr Zhivago, and a two-part serialisation of DH Lawrence's Sons & Lovers, which began last night.
It has not been all bad news for ITV, however. The network is said to have maintained its lead over BBC One in the peaktime schedule in 2002. ITV's share of the audience averaged 31.5% compared to BBC One's 27.9%, according to unoffical overnights published in Marketing.
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