Media agencies said advertisers, particularly in food and retail, are looking to cut adspend because of sterling’s slump and rising inflation.
Procter & Gamble is believed to have slashed its TV adspend in the UK because of currency pressures.
Media buyers report that the TV market looks to have ended 2016 just better than flat, with growth of about 0.5%, defying the doom-mongers who expected a decline.
December was up about 5%, helping to offset an almost 5% slump in September, October and November in the aftermath of the referendum vote.
TV sources suggest ad revenues are likely to fall about 2% this year, which would mark the first decline since the 2008-2009 recession. However, one buyer cautioned that it is "probably the most unpredictable market for years".
Analysts at Deloitte remain optimistic, forecasting this week that the TV ad market will be flat in 2017.
Ed Shedd, head of technology, media and telecommunications at Deloitte, said "the death of television has been declared all too often" but the medium is "capable of delivering, on a daily basis, audiences in the millions".
ITV launched two big entertainment shows this month – The Voice UK and Dance Dance Dance.