English and French clubs formalised plans for their own breakaway European club championship on Sunday, naming the proposed new competition the "Rugby Champions Cup'' and inviting teams from the rival Six Nations countries to join them.
Premiership Rugby - the umbrella body representing England's top-flight clubs - said a working group had been set up to ensure the competition would be ready "in good time'' for the start of next season.
"The competition will be based on the principles of qualification on merit, a strong competition format, equality between the leagues, higher commercial values for the teams and expansion into new European markets,'' the statement read.
The leading teams in England and France are pressing ahead with plans for the new continental competition after seeing talks repeatedly break down over a revamp of the structure of the Heineken Cup, Europe's current top-tier club tournament.
They are unhappy at sides from Wales, Scotland, Ireland and Italy getting guaranteed spots in the competition, while a dispute over TV rights in Britain has left the Heineken Cup on an even more precarious footing.
Teams in England's Premiership and France's Top 14 announced on September 10 that negotiations were at an end, and that the two leagues were looking to set up a rival competition to the Heineken Cup.
"The Rugby Champions Cup will be open to teams from all three leagues in Europe,'' the Premiership Rugby statement said, referring to the Pro12 league that consists of clubs from Ireland, Wales, Scotland and Italy.
More details on the competition format and financial aspects will be revealed next month.
The new tournament would need approval from the IRB, rugby's world governing body, before it can begin.
The equivalent of football's Champions League, the Heineken Cup has been running since the 1995/96 season and has expanded into a popular 24-team competition featuring the top teams from the Six Nations countries. Its current deal runs through to the end of this season.
European Rugby Cup, which runs the Heineken Cup, and the clubs of the Pro12 have given little indication of conceding ground in the fight for the competition's future.