Media groups have warned that advertisers have been blacklisting news over ill-founded fears that their brands are damaged by being displayed close to certain stories, leading to concerns about the effect on future funding for important journalism.

A study carried out by US-based marketing group Stagwell said that “news has been systematically demonetized and faces significant bias” compared with more “favourable advertising environments” such as sports and entertainment.

News websites have been hit by the widespread use of software that sets out hundreds of key subjects and words to avoid in the automated process of placing advertisements against stories. In other cases, marketers simply want to avoid straight news stories in the belief that people are less likely to feel favourable to their brands than if they were advertising alongside entertainment stories.