Ben Walmsley, digital commercial director at The Bridge, the commercial arm of the publisher, was speaking on a panel on "Rebuilding trust and delivering transparency, suitability and viewability" at Campaign’s Digital Media Strategies conference in London.
He told the audience: "We did a test where we turned off all our programmatic supply and tried to buy our own inventory when it wasn’t available, and we found that we could.
"In one particular exchange there was somewhere between £750,000-£1m a month worth of inventory being sold in the name of The Sun and The Times. That’s just one publisher in one exchange."
He added that while this experiment had shed light on the scale of the problem facing both publishers and buyers, he was confident that ads.text, the Authorised Digitala Sellers programme from the IAB Tech Lab, would have a positive impact.
Walmsley was speaking alongside Sue Unerman, chief transformation officer at MediaCom, Phil Smith, director general of ISBA and Sam Tomlinson, partner, media insight and assurance at PwC UK, in a discussion chaired by Campaign global head of media Gideon Spanier.
Discussing the progress made to improve industry practices over the past year, Tomlinson welcomed the "more informed conversation" between publishers, advertisers and agencies, and that there was "less finger pointing and a more positive and collaborative tone by all parties."
The tech giants had woken up the flaws in their worldview, Unerman said: "They are built on a utopian ideal that everyone should have access to everything, and so the idea that some sectors need protecting more than others was against that idea.
"I’m very pleased that the more vulnerable are going to be protected and Google and Facebook are starting to see the need for that."
Smith said that while brands and agencies had made progress in creating transparent relationships, the industry was only 30-40% of the way to where it needed to be. "Agencies and advertisers have different interests," he said. "The challenge is to create an alignment of interests so that agencies do well when clients do well."
On the YouTube brand safety issues that saw large numbers of advertisers abandon the video platform last year, Smith said brands had used the situation to assess what made sense for them.
"I’ve still got many members who are not back on YouTube," he said. "Others who are imposing very strong whitelists, and doing deals direct as well. Every advertiser is taking a different run at it."
Defending the role of media agencies in the ecosystem, Unerman said: "What we’ve got is accumulated expertise – experience from related brands and sectors.
Tomlinson, responding to comments from P&G’s Marc Pritchard that the FMCG company would bring more media handling in-house, added: "If you’re P&G you can do that. If you’re Unilever you can do that. I’m not sure how many advertisers that applies to. Because you need that breadth of experience [of media agencies]."