Another 100 companies have reportedly pulled their advertising from the far-right news site Breitbart, as the momentum builds behind a grassroots campaign calling on advertisers to boycott the site.

Audi, Visa, T Mobile and Lufthansa have joined the growing list of companies to withdraw, according to Sleeping Giants, the group behind the campaign, which claims that at least 1,250 advertisers no longer wish to be associated with it.

Campaigners have successfully encouraged Twitter users to name and shame companies who advertise on the site by posting screenshots of Breitbart ads.

As advertising is often purchased through third-party agencies, companies may be completely unaware that their ads will end up on the Breitbart site.

Breitbart “declared war” on Kellogg’s last year, after the cereal company announced that it would be blacklisting sites that “aren’t aligned with our values”.

Responding to the statement, editors urged Breitbart readers to boycott all Kellogg’s products.

Sleeping Giants’ announcement comes after a week of bad press for Breitbart.

On Tuesday, Milo Yiannopoulos, a senior editor and well known figurehead for the site, was forced to resign his position after remarks surfaced in which seemed to condone paedophilia.

Milo Yiannopoulous defends relationships between younger boys and older men on radio show

A source told Fox Business of their concern that the public campaign and the Milo scandal would have a tangible impact on the site’s revenue.

Breitbart "was already in trouble with advertisers" a source close to the company, told the broadcaster, adding that "Milo made the battle much more difficult.”

They added that the association with Mr Trump's senior adviser Steve Bannon, its former executive chair, was also hurting the company. Mr Bannon has previously described Breitbart as "the platform for the alt-right".

In an effort to combat dwindling ad revenue, Breitbart appears to be attempting to re-brand as a more moderate platform.

Recent hires from mainstream publications like The Wall Street Journal and The Hill website, indicate editors will increasingly be focusing on straight news reporting and moving away from its notoriously fiery comment pieces.

Emma Pullman, lead strategist campaign group SumOfUs, who are also putting pressure on advertisers to boycott Breitbart, told The Independent that the campaign was “reaching fever pitch”.

This is a really tangible way people can convince companies to not advertise and it's also a way to criticise the rise of the far-right and the hatred, xenophobia and racism that is coming out of Breitbart."