LONDON: There are signs of growing unease in advertising circles about the impact of June's Brexit vote, with industry sources warning that fourth quarter TV advertising revenues could be significantly down on last year.

Media sources indicated to Campaign that TV ad revenues are set to decline by 8% in October and 7% in November, following a 5% fall in September.

A TV source said: "November looks to be the most significant because it is the first 'clean' month since Brexit with no unusual comparative with last year" – a reference to the Rugby World Cup which finished at the end of October 2015.

The Guardian's contacts were telling a similar story, with October figures expected to be down 5% and one observer suggesting they were worse than appeared at first sight since they include ITV VOD advertising figures for the first time.

A TV executive explicitly cited continued uncertainty after the EU referendum.

"Since about four or five weeks ago things have got very tough," they said. "It is not structurally about the TV advertising model versus other media such as online. TV ad spend is healthy in other markets, here it is about fears over Brexit hurting the market."

The Guardian's sources suggested the TV ad market could shrink between 1% and 2% over the whole year.

"It's difficult to see how even a bumper Christmas spend will save 2016's figures, which at the start of the year were predicted to be very strong," said a senior advertising executive. "It looks like it will be a big fall versus forecasts and at this point 2017 looks like it will contract as well."

First quarter TV adspend hit a record high of £1.3bn, according to official data in the Advertising Association/Warc Expenditure Report; full-year forecasts, however, were lowered 1.5 percentage points to 3.6% growth following the referendum result. The Q2 figures are due to be published on Tuesday.

Data sourced from Campaign, Guardian; additional content by Warc staff