Channel 4 has poached the Channel 5 owner Paramount’s £300m-plus TV advertising sales business from Sky, in a huge boost days after the broadcaster announced it is to cut 340 jobs.

The win is a big win for Channel 4, which relies on advertising for about 90% of its £1bn in revenues.

It comes as the broadcaster, which also handles the ad sales for UKTV, the owner of channels including Gold and Dave, moves to reduce its headcount of 1,276 by more than a quarter in the biggest round of job cuts in its history.

The deal with Channel 4 marks the first time that the advertising for the two public service broadcasters has been sold together.

As well as ad sales for Channel 5 – Paramount’s biggest ad sales business in the UK – Channel 4 will also be responsible for promotional slots with brands including MTV, Comedy Central and Nickelodeon.

However, the deal does not include ad sales for the streaming service Paramount+, which is home to hits such as Yellowstone, MobLand and Uefa Champions League matches from next year, or on the free ad-supported streamer Pluto TV.

“This exciting partnership, which brings together ad sales for Channel 4 and 5 for the first time, creates a tremendous proposition for advertisers, rooted in the power of public service broadcasting,” said the Channel 4 chief executive, Priya Dogra.

“This groundbreaking collaboration will give advertisers seamless access to a unique portfolio of trusted, premium brands and even larger audiences. It will also generate new commercial opportunities for two distinctive commercial PSBs, helping support further investment in British programming.”

Reemah Sakaan, the president of Channel 5, described the deal as “a historic partnership between two British broadcasters”.

While the loss of the business is a blow to Sky, it is also likely to help its attempt to get regulatory clearance for its £1.6bn takeover of ITV’s TV and streaming business.

Sky’s takeover of ITV will lead to the enlarged business accounting for more than 70% of the traditional TV ad sales market – including digital sales on broadcasters’ streaming services and third-party deals such as selling Channel 5’s inventory – which would have left Channel 4 as a distant second player at about 26%.

Sky and ITV have been lobbying that the competition regulator should consider a much wider market definition, with the combined entity accounting for just more than 30% of the overall video advertising.

While the move to Channel 4 is understood to have been made for purely commercial reasons, it comes two years after Sky Media, the broadcaster’s sales arm, uncovered miscalculations that resulted in partners not receiving the correct revenue from their deals.

Paramount and Channel 5 were the biggest partners affected, with the overall miscalculations understood to be about £300m in missed payments dating to 2017 that needed to be reimbursed.

Sky has paid Paramount £98m in relation to the miscalculations, according to Channel 5’s annual reports for 2023 and 2024.