MONTREAL, Canada - Rumours that Pirelli will leave Formula 1 at the end of the 2013 season are growing by the day.The Italian tyre-maker, taking heavy criticism for its crumbly 2013 tyres and now embroiled in a squabble over allegedly illegal tyre-testing, is also unhappy with F1's tight testing limits and the obstacles to tyre specification tweaks being erected by some teams.Mercedes' team boss Ross Brawn, facing the wrath of a tribunal for accepting Pirelli's invitation to a private (depending on who you believe) tyre-test after the Barcelona GP, was uncertain whether Pirelli would remain with F1.'CANNOT WORK IN THE DARK'"Discussions about testing for 2014 will certainly be beneficial for whoever the tyre supplier is in the future," he said.Italy's La Repubblica said Pirelli's Paul Hembery repeated his company's recent quit threat on Friday... "if we are unable to do some tests with the new tyres before the start of the season"."We cannot continue to work in the dark," he added. "By September 1 we need to provide the specifications for next year but we don't even know what the cars are going to be like."We believe the (2014) tyre should be wider but we don't know by how much. This year, because of the lack of tests... we ended up with these cases of de-lamination, and then because we couldn't go on a track we had to remedy it in the laboratory."Still the teams refuse to agree to the new tyres debuting at June's British GP at Silverstone."We've heard that Lotus will not accept any changes," Hembery was quoted as saying by Finland's MTV3. "If that's right, we will use the same tyres for the rest of the season. There may be some more four-stop races, but what can we do?"Indeed, Hembery said Pirelli may have to revert to using glue during the construction of the unchanged 2013 tyres to stop the tread separating from the carcass."Either we get the agreement of all the teams, which I think is unlikely," he said, "or we will have to have some other ideas."'WE FOLLOWED RULES'He was quoted by Italy's La Repubblica thus: "We don't want to have another season like this one. Our (F1) contract is expiring. Will F1 be without tyres? I don't know, but that's not our business."Who knows, maybe they'll find another supplier willing to work in the dark."Even Pirelli president Marco Tronchetti Provera is being asked about the tyre-testing squabble, telling Tuttosport: "It doesn't concern us. We've followed the rules and will continue to do so."Hembery, on the other hand, sees the situation as the moment to set out Pirelli's conditions for staying beyond 2013. "We will wait for the tribunal (which some say could be fast-tracked to sit before the end of June) but then there will be several elements that need to be discussed. We are talking about issues that have a clear impact on our business."'SECRET AGENDA?'He told Canada's La Presse: "This is not only a matter of waiting for the truth to come out but also a question of doing things differently."Germany's Auto Motor und Sport, meanwhile, took the opportunity to float a conspiracy theory. Correspondent Michael Schmidt wondered: "Does Jean Todt have a secret agenda... does he want Pirelli to get so angry that it leaves voluntarily, opening the door to Michelin?" Stay with Wheels24 for the 2013 Canadian GP weekend.