The future of European rugby at the end of the 2013-2014 season is unclear after English and French clubs moved to set up a Rugby Champions Cup to rival the Heineken Cup, with the new competition run by clubs rather than the unions.
BBC Scrum V looks at the issues and the interested parties involved in the dispute which is threatening to tear European rugby apart.
Why has there been a threat to the future of the Heineken Cup?
There had been discontent in England and France going back to
on how the European competitions, the Heineken Cup and the Amlin Cup, were organised.
The English Premiership Rugby and French Top 14 clubs, who both "served notice of withdrawal from the ERC Accord", are unhappy at how teams qualify for the Heineken Cup especially from the RaboDirect Pro12 league and how proceeds are shared.
European Rugby Cup (ERC) is the governing body and organiser of the Heineken Cup and Amlin Challenge Cup tournaments.
is dominated by representatives from Six Nations national governing bodies who outnumber the independent representatives from the French Top 14 clubs, Premiership Rugby and Regional Rugby Wales.
2013-14 Heineken Cup structure
7 (Castres, Toulon, Toulouse, Clermont-Auvergne, Racing Metro, Montpellier, Perpignan)
6 (Northampton, Exeter, Saracens, Harlequins, Leicester, Gloucester)
4 (Leinster, Connacht, Ulster, Munster)
3 (Ospreys, Cardiff Blues, Scarlets)
2 (Glasgow, Edinburgh)
2 (Zebre, Treviso)
Only the top six clubs in England and France are guaranteed a place in the Heineken Cup, whereas at least 10 Pro12 outfits - including both Scottish teams, both Italian teams and a minimum of three sides each from Wales and Ireland - have automatic entry into the competition.
The English and French clubs are also unhappy about how the revenue is split.
Of the £44m generated by the 2012-2013 Heineken Cup, 52% went to Pro12 clubs while 48% was shared by England and France, who want a three-way split of revenue between the Aviva Premiership, Ligue Nationale de Rugby and Pro12.
How would the Rugby Champions Cup be run?
England and France are proposing a 20-club tournament run by the clubs rather than the unions.
In addition, they would set up a second-tier competition of 20 teams, to replace the existing Amlin Challenge Cup, as well as a "development" competition, which could include sides from Spain, Portugal and Russia.
All Pro12 clubs - from Wales, Scotland, Ireland and Italy - currently participating in the Heineken Cup and Amlin Challenge Cup have been invited to join the Anglo-French breakaway competition.
Who is involved in the dispute?
There are various interested parties including clubs/regions, leagues, respective unions, ERC, the International Rugby Board and TV companies (BT and BSkyB).
The English and French clubs insist the proposed Rugby Champions Cup should be run by the clubs, not the unions, which would go against the grain of the current European Rugby Cup structure.
There is a sense that the Celtic nations and Italy would be in a position to compromise on the demands by the English and French for a three-way split of revenues and merit-based qualification from the Pro12.
Scrum V's Ross Harries guides us through the issues and personalities involved in the row over the future of the European Cup.
Welsh, Scottish and Irish Rugby Unions
had insisted their clubs would not participate in any European competition unless it had the "full approval" of the International Rugby Board (IRB).
IRB has indicated
to the BBC it would probably support a new competition if approved by the English and French unions.
The English Rugby Football Union (RFU) is still uncommitted to the new tournament and its French counterpart actively opposed it.
What are the implications for RaboDirect Pro12 teams in Wales, Scotland and Ireland?
Uncertainty surrounding the future of the Heineken Cup has caused concern among the Celtic nations.
In Wales, there are worries about keeping and signing players.
Cardiff Blues, for example, have not been able to offer Sam Warburton a new contract for the 2014 season
because they are uncertain of what budget they will have.
The Welsh regions stand to lose £1m each per year if they are not involved in European competitions next season.
But, it is unlikely the four Welsh regions would sacrifice their place in the Pro12 competition to play in the Champions Cup because it would not pay enough. They would face being disciplined by the WRU if they rebelled.
In addition, the Champions Cup alone would not give the four Welsh regions enough competition and revenue, as they are excluded from England's Aviva Premiership.
However, the Welsh regions have
backed the idea of
the revamped European competition from next season.
Their umbrella body, Rugby Regional Wales says some new tournament details need finalising, but added: "It is now clear there are a number of significant advantages to the new competitions."
Meanwhile former national captain
Andy Nicol believes professional rugby union in Scotland could end
if there is no European competition next season.
"It could well be the end of professional rugby in Scotland if the competition wasn't to go ahead," he said.
"I don't think you can fill a hole of that amount with anything else."
There have also been concerns from Ireland, with Leinster chief executive
Mick Dawson admitting the province would have to consider entering the new competition
if no solution is found.
Premiership Rugby deputy chairman
Bruce Craig believes every Pro12 team is prepared to sign up to the new competition,
but they are being held back by their national governing bodies.
He has warned the national unions from interfering, and also indicated that they and the IRB could face court action if they attempt to stop the Rugby Champions Cup.
Recent Heineken Cup winners
: Munster (Ireland)
What are the implications for the TV companies?
BT paid £152m for rights to broadcast English club rugby including their participation in a European tournament. But crucially, the deal excluded the Heineken Cup.
Soon after, ERC
signed a four-year extension to its TV deal
with Sky Sports.
ERC has accused the English clubs of reneging on a binding contract in favour of a "questionable TV deal".
But Premiership Rugby disputes this, and has told the BBC that the TV conflict is a "distraction". Premiership Rugby believes that as it served notice in June 2012, ERC had no right to negotiate an extension to the current deal after that point.
What next for the dispute?
A meeting on Wednesday, 23 October attended by the governing bodies, but not the top English and French clubs nor the Welsh regions,
proposed the formation of two tweaked European competitions of 20 teams each as well as a change in revenue distribution.
English and French clubs would share 13 places in the revamped top-level competition, with fewer automatic qualification spots for the other nations.
ERC had already appointed an independent mediator -
Canadian barrister Graeme Mew
- in an attempt to resolve the row.
The ERC's Jean-Pierre Lux said Mew's appointment is "a hugely valuable opportunity to find an agreed solution which will benefit all European club rugby stakeholders".
The BBC has also learnt that England's RFU had been working hard behind the scenes with clubs and unions to try to find a resolution.
ERC meanwhile insists there is still time to save the Heineken Cup, saying the notice period still has seven months to run.
The Scottish, Welsh, Irish, French and Italian unions
met in Dublin in November
and insisted the Heineken Cup would go ahead despite breakaway plans.
The unions issued a joint statement saying they stood "side by side" in their belief that the unions, rather than clubs, must be "at the heart of the governance of cross-border club competitions".
England's Rugby Football Union (RFU) was "extremely disappointed" not to be part of the discussions, but said it was committed to finding "a solution so that a truly pan-European competition can continue to thrive for the benefit of players and spectators alike".
Premiership Rugby chief executive Mark McCafferty said despite the stance of their unions, French and Welsh clubs were still behind the breakaway.
"We don't see any evidence of their support wavering. We were working with them on Wednesday on the implementation of the Champions Cup," McCafferty said.
"I'm also confident that the Welsh regions remain in support of the Rugby Champions Cup," he added.