Rival publishers News UK, the Guardian and the Telegraph have co-founded The Verified Marketplace, a joint sales house for premium outstream video.

The marketplace will allow advertisers to buy desktop and mobile outstream video inventory across the four nationals – the Sun, the Times, the Guardian and the Telegraph – instead of navigating with individual sales teams. An outstream video ad unit is a large format video player usually situated within an article that autoplays as a user scrolls over it.

The marketplace will be powered by UnrulyX, Unruly's viewable video supply-side platform (SSP). The video ads will be independently verified by Integral Ad Science and MOAT.

It is claiming it will offer a potential audience of more than 39 million unique users across the four publisher sites.

The marketplace has been founded to meet what Hamish Nicklin, chief revenue officer at the Guardian News & Media, said was a "clear demand from advertisers for high quality video inventory and greater media collaboration to make buying easier and more effective".

Jason Trout, Unruly’s managing director for EMEA, said the marketplace will deliver high-quality ad formats and "peace of mind" to advertisers at a time when trust in the programmatic ecosystem has "never been lower".

Ben Walmsley, digital commercial director, News UK, said: “With the introduction of The Verified Marketplace we have created a safe medium for advertisers who want to access verified inventory at scale. It is an encouraging development from the news brands that will give advertisers access to quality audiences on one single platform.”

The initiative has been backed by GroupM, which said it will continue to push for greater levels of collaboration from publishers in order to bring its clients "quality media with the ability to transact at scale”, said Robin O’Neill, the group's managing director.