The Scottish, Welsh, Irish, French and Italian rugby unions have committed to the existing European competitions.
The decision means the competitions could go ahead without the English clubs next season.
And crucially, the Premiership clubs insist they still plan to press ahead with a new competition, the Rugby Champions Cup.
The five unions say they stand "side by side" in driving a European club competition next season under the auspices of European Rugby Cup following talks in Dublin on Thursday.
In a statement the five unions - which did not include the Rugby Football Union - said they had agreed the following: "A European club competition is to take place during the 2014/2015 season following an optimised sporting and economic format with 20 teams, no matter how many countries are involved.
"The competition will be driven by the existing organisation (currently named ERC) which will remain in charge of the centralised sale and management of all commercial rights, amongst other things.
"Discussions over governance will be pursued in order to optimise the internal functioning of the existing organisation (currently named ERC).
"The common aim is to move eventually towards the integration of European competitions within an all-encompassing European rugby framework."
The English and French clubs had proposed a breakaway competition from next season, and were supported by the four Welsh regions.
But the Welsh Rugby Union (WRU) and the French Rugby Federation (FFR) have stated they stand together with the Italian Rugby Federation (FIR), Irish Rugby Football Union (IRFU) and Scottish Rugby Union (SRU) for European club competitions.
The RFU later issued a statement expressing their dismay that they were excluded from the meeting, despite chief executive Ian Ritchie being present at the negotiations in October that were attended by all six unions and ended with broad agreement on certain principles.
However, the way in which European club competition is governed is proving a critical stumbling block.
"We are extremely surprised and disappointed not to be involved," an RFU statement read.
"It is right that the outcomes of the mediated meeting held in Dublin on October 24, which resulted in an agreement for a meritocratic tournament and equitable distribution of revenues, have been reaffirmed.
"It has been clear for some time that governance is a central outstanding issue.
"We remain committed to help facilitate a solution so that a truly pan European competition can continue to thrive for the benefit of players and spectators alike."
Premiership Rugby responded to the unions' position by reconfirming their intent to launch the breakaway Rugby Champions Cup.
"Premiership Rugby notes the statement issued this evening concerning the proposed new European club rugby competitions for the 2014/15 season," read a statement released by Premiership Rugby.
"There is no detail concerning the teams involved or the competition format given the absence of so many teams.
"The English and French clubs served notice on ERC and its competitions on 1st June 2012 and the required notice period concludes after the end of this season when the Accord will terminate.
"Today's announcement would appear to indicate that the latest negotiations have been ended, as was the case in September 2013.
"As a result, we shall continue to implement the plans under way for the Rugby Champions Cup with the declared participants in time for the 2014-15 season."