Advertising expenditure in the UK is set to rise by 6% to £24bn in 2020, marginally lower than previous forecasts made by Dentsu Aegis Network.
The holding company previously predicted UK adspend to rise by 6.6%.
Dentsu Aegis’ latest Ad Spend report, published today, also noted a slight downward revision for 2019. In June, it forecast a rise of 6.3% but now reports a 6.1% increase to £22.6bn.
"With political and Brexit uncertainty likely to continue through Q1 2020, we expect another turbulent economic year next year," the report said.
For 2021, Dentsu Aegis expects adspend to stay stable and rise by 6.3%.
This UK growth is down to spend in digital, which has increased by 9.2% – two-thirds of the total advertising market. Mobile will grow by 16.9%, according to the report, and make up 60% of the total digital advertising market.
Dentsu Aegis added that 2020 will be a "big sporting year" with the upcoming Uefa Euro 2020 football tournament and the Olympic Games in Tokyo. The winter Love Island is also likely to give ITV a boost in ad revenue, the report added.
It said: "With the semi-final and final of Euro 2020 taking place at Wembley and high hopes for a strong England team performance, we expect to see strong viewing figures and a boost to TV revenues in 2020."
As a result, TV is forecast to return to growth at 1% in 2020, with video-on-demand set to be a "key driver" in the increase this year and in 2021.
Radio and out-of-home are expected to grow 3% each this year.
Globally, Dentsu Aegis expects adspend to rise by 3.9% to $615.4bn (£471.5bn), up from 2.6% growth last year.