Media sources said January and February are both due to drop 5%, while March could be down as much as 10% because of tough comparisons a year ago, when Easter was early.
April is now seen as a crucial test for the TV market because Easter falls late this year.
TV ad revenues fell 8% in April 2016 in the first sign of advertisers’ anxiety ahead of the referendum. They then declined heavily in September, October and November, before recovering in December.
Media buyers were closely watching a dispute between Discovery and Sky this week. Discovery threatened to pull its 12 channels from the Sky platform from 31 January in a row about its carriage deal, which could have had a knock-on effect on TV audiences and the ad market. But the two sides were poised to agree a peace deal as Campaign went to press.
Industry sources have been warning that TV ad revenues are likely to fall in 2017 for the first time since 2009, even though official forecasts remain optimistic.
A report from the Advertising Association and Warc this week predicted TV adspend growth of 1.6% in 2017. Spot revenue was forecast to be up 0.7%, with video-on-demand revenue rising 12.4%.