The leading English and French clubs have written to the organisers of the Heineken Cup confirming they will not be attending next month's talks in Dublin which were arranged to find a way of saving the tournament.

Premiership Rugby and Ligue Nationale de Rugby are pressing ahead with organising replacements for the Heineken Cup and the Amlin Challenge Cup with a warning to the three Celtic unions and Italy that they face financial meltdown if they refuse to allow their clubs to take part.

The 23-24 October meeting was arranged by European Rugby Cup Ltd to break 15 months of deadlock and it has hired a mediator, the Canadian lawyer Graeme Mew, to find a way of bringing the unions and the French and English clubs together – a plan that looks doomed to failure.

"We have had an email from Mr Mew and our response is that, as we have no dispute with ERC, there is nothing to mediate over," said the Premiership Rugby chief executive, Mark McCafferty. "We and the French clubs have put that in writing and we have declined the Dublin invitation.

"ERC is finished. Its competitions have gone and our focus is on setting up the Rugby Champions Cup as it takes a lot of effort to put everything in place. We want all the teams from the six countries involved in the Heineken Cup to take part but it will be run by the clubs with safeguards put in place to ensure it does not cut across international rugby."

Meanwhile the Celtic unions and Italy, who make up the RaboDirect Pro 12, all issued statements on Wednesday which said they remained committed to a pan-European competition and that they would not allow their professional teams to take part in tournaments which did not have the full approval of the International Rugby Board and the relevant unions.

None of the four unions mentioned ERC or said unequivocally they would have nothing to do with the Rugby Champions Cup. The English and French clubs will not be playing in the Heineken Cup next season, even if the Rugby Champions Cup is proscribed by the IRB. ERC would struggle to survive, unless someone generously backed what would effectively be a RaboDirect Cup.

The French and English clubs want ERC to fold because it would mean that its contractual obligations, such as the television contract to Sky, which clashes with the BT deal signed by Premiership Rugby last year, would perish with it. That said, the directors of ERC, which include representatives from Premiership Rugby and LNR, have been given legal advice about the potential consequences to them of winding up the organising body if it is a means of evading legally binding commitments.

It is one reason why Premiership Rugby and LNR have decided not to attend any more ERC meetings and, significantly, they served notice they were pulling out before the contract extension with Sky was signed. They are prepared to talk to the RaboDirect unions directly, with McCafferty pointing out that no one's interests would be served if there was no European club rugby next season.

There has been interest in the Rugby Champions Cup from Wales and Ireland, although Ireland's four provinces have been ordered by their union not to make public comments on the Heineken Cup after the Leinster chief executive, Mick Dawson, said this month that they would have to consider how to get into the new tournament if "everything went pear-shaped".

McCafferty said: "No European competitions next season would be a financial catastrophe for Celtic rugby. If the unions try to block the Rugby Champions Cup, they have to offer something else but there is no way we or the French clubs will be part of an organisation that is controlled by unions.

"All we are looking to do is maximise the value of European club rugby, not take over the game. We would work with the unions, ensuring everything fitted in around the international calendar, but we will no longer work for them. It will happen sooner or later and no one wants this to end up in court."