England's leading three sides will only enter the fray in 1996-97 because their fixtures for next season cannot be changed.
The championship, which will be "organised, regulated and run by the Five Nations Committee and not by any outside agency", ends months of speculation about breakaway movements and unofficial, circus-style tournaments. There will be no prize- money.
"I'm delighted we are there at last after nine months of hard work," Vernon Pugh, the Welsh Rugby Union chairman, said.
"It could have been earlier if some clubs hadn't muddied the waters, but it will be a good thing for the European club game.
The formula for Welsh representation will be decided this week. It is likely to be a shoot-out between the top three teams in the Heineken League First Division or the top two league teams and the Swalec Cup winners.
The French will be entering their cup winners and the top two league clubs, while the three representatives from Scotland and Ireland are likely to be provincial teams.
The Italians are likely to be granted two places, with Michael Lynagh's Treviso, Wayne Shelford's Rome and Diego Dominguez's Milan sides battling it out for the places, while the Romanians will enter their top club side.
"The tournament will run from October to December, under the format of four pools of three teams each," Pugh said.Reuse content