Channel 4 will announce plans this week for deeper-than-expected job cuts amid a steep downturn in the broadcast advertising market.

Sky News has learnt that the state-owned broadcaster will say on Monday that it is cutting nearly 250 roles, a figure equating to just over 15% of its full-time workforce of more than 1,300 people.

Industry sources said this weekend that while the number of people being made redundant would be approximately 200, in line with earlier reports of the cost-cutting, close to an additional 50 roles were also being axed by chief executive Alex Mahon.

It is expected to be the biggest bloodletting in the history of Channel 4, which launched in 1982 and which came close to being privatised last year.

Ministers ultimately decided against selling the company despite having hired bankers from JP Morgan to oversee an auction.

This week’s job cuts will affect a range of departments at the Gogglebox and Great British Bake-Off producer.

Ms Mahon has described the ad market’s decline as “market shock territory” for the company.

A Channel 4 spokesperson said it was “a wholly commercially funded and self-reliant broadcaster known for producing iconoclastic programmes and generating enormous value for the UK creative economy”.

“Like every organisation, we are having to deal with an extremely uncertain economy in the short term and the need to accelerate our transformation to become a wholly digital public service broadcaster in the long term.

“As a result, we need to continue to divest from our linear channels business and simplify our operations to become a leaner organisation.”