Telegraph Media Group, publisher of the flagship broadsheet, The Daily Telegraph, and its sister newspaper, The Sunday Telegraph, announced it will no longer be participating in “Project Arena,” a planned consortium of the newspaper publishers.

Arena was launched last year with the goal of combating the dominance of the big tech platforms in digital ads by offering advertisers access to their combined digital ad inventory and data.

TMG’s departure follows the previous withdrawals of two other big newspaper publishers: Daily Mail & General Trust, publisher of the Daily Mail and Mail on Sunday, as well as the free tabloid Metro, and Trinity Mirror plc, publisher of 150 newspapers, including the Daily Mirror along with regional dailies like the Manchester Evening News and Bristol Post.

The departures are a significant blow to the alliance, which like other such efforts, principally aimed to achieve scale sufficient to compete with the platforms. The Daily Mail site alone attracts 243 million unique visitors per month globally, while Trinity Mirror’s combined sites draw 110 million uniques. The Telegraph claims over 84 million inquires across its properties.

Although these figures probably overlap, they also represent the lion’s share of the total unique visitors claimed by Project Arena. Currently, the consortium still counts two publishers, News UK, publisher of The Times and The Sun, and the Guardian Media Group, publisher of The Guardian, as participants.

Earlier this year, News UK reported the Sun Online attracted 25.4 million unique visitors per month in the UK, while The Times site has around 22.7 million unique visitors on mobile in the country. The Guardian Website has 22.6 million unique visitors in the UK and over 120 million unique visitors per month globally.

Newspaper publishers in other countries are pressing ahead with plans for alliances.

Earlier this month, French publishers and media companies announced plans for a new consortium to challenge the duopoly, called the Gravity Alliance, with a total of 15 media companies on board.

The list includes Lagardère, which owns Paris Match and the French edition of Elle, as well as radio and TV stations and sports and entertainment franchises; Condé Nast’s French business; Les Echos Group, publisher of a major business daily, L’Équipe, a leading sports newspaper; and SoLocal, a large classifieds publisher.