Although Pirelli agreed a new three-year contract in October last year, it has yet to be officially signed off by the FIA.

Though the sport's governing body insists there is not an issue, the Italian manufacturer is concerned because the proposed rule changes for 2017, which are aimed at making the cars around five seconds a lap faster, will mean higher cornering speeds and heavier loads, the result of increased downforce.

With strict limits on testing, Pirelli has called for extra days, with leading drivers, and an agreement on a car to be used. It is these specific demands that are causing the delay in signing off the contract.

"Pirelli wanted the targets that they were asked to achieve to be put into the contract," Technical Delegate and Race Director, Charlie Whiting, told reporters at the weekend in Bahrain. "They want more specific items in the contract regarding testing. They really just want a guarantee of testing.

"If we are going to set them targets, they want the tools with which to achieve those targets," he continued. "Those are really the only points. I think everything else is sorted but they just want this guarantee of tests.

"We've put it into the regulations but they'd like a little comfort and also the possibility to test with their own car. I think it’s all quite achievable in the short term."

In January, Pirelli hosted a meeting at its Milan HQ attended by Jean Todt, Bernie Ecclestone, a number of team bosses as well as Sebastian Vettel, Nico Rosberg, Felipe Massa and several other drivers. The tyre manufacturer made it clear that it is willing and able to provide the sort of tyres the drivers are pushing for but insists that the teams must agree to additional testing.

Of course, the situation hasn't been helped by the failure to agree the final 2017 regulations, the deadline, after a couple of false-starts, now set for 30 April.

"It is very important to define what the sport wants," Pirelli Motorsport boss, Paul Hembery, told Motorsport.com at the time. "We are happy to deliver exactly what everyone wants – but it does require testing time that is done in a logical and sensible fashion.

"All we want is to have clarity from stakeholders on what they want and we want to let them know what we need to deliver that. We've described already that we want 30,000km of testing, and we are happy to start with an old Toyota or Lotus and combine it with a modified chassis later in the year to confirm the work we have been able to do.

"In 2017 the technical aspects will become even more complex, so Pirelli is even more convinced of the need to carry out more on-track testing. This is a factor that has been extremely limited in recent years, despite the important evolution of the cars and subsequent increase in performance. All these are vital steps towards tyre development that takes into account the future evolution of the cars and added performance, which will be particularly notable in 2017."