Martin Brundle has claimed that the ongoing accusations of an 'illegal' test conducted by Pirelli and Mercedes only serves to underline the limitations being faced by the tyre supplier.

Pirelli has long campaigned to be allowed access to a contemporary F1 car in order to ensure that its tyres are suitable for the sport, but has instead been saddled with a string of out-dated machinery that has fallen short of the standard required.

As a result, this year's tyres have, by the company's own admission, been 'too aggressive', suffering excessive wear and delamination problems, and prompting the introduction of a revised tyre for next month's Canadian Grand Prix. Despite the test carried out by Pirelli and Mercedes in Barcelona immediately after the Spanish Grand Prix ostensibly being to work on compounds and construction destined for next season, the Italian company also revealed that the Montreal rubber was thrown into the mix, although Mercedes, it insists, was never party to which tyre was being run at any given time.

Mercedes team boss Ross Brawn says that there was no intention of keeping the test 'secret', as he been alleged by rivals, pointing out that they should have realised that the Silver Arrows were not packing up after the Spanish Grand Prix, but it has emerged that rules regarding running a 2013 car and conducting the test 'in season' may have broken conditions laid down by the governing body.

Brundle, however, insists that the row would never have been an issue had Pirelli been supplied with a car up to the task of carrying out the tests independently.

"[The] 'secret' Mercedes test has highlighted the lunacy that Pirelli don't have access to relevant F1 test car so no ability to develop the tyres," he wrote on his Twitter feed.

"Unfortunately, the 2012 HRT was barely fast enough to get out of its own way, so it wouldn't be a representative Pirelli test car. Even the ex-Toyota Pirelli test car I drove in Jerez two years ago had been heavily modified to generate representative latest downforce levels."

Pirelli motorsport director Paul Hembery admitted during Thursday's FIA press conference in Monaco that the cars currently available to the company were a long way from the performance of current machines.

"They're probably closer to the 2011 cars with the blown diffusers," he revealed, "The [current cars are] going, certainly, a little bit harder than we anticipated this season. We're probably lapping our 2010 car three to four seconds slower, for example. That gives you an indication that we're not stressing the tyres during our testing as much as the cars are today."

With the F1 rules changing for 2014, Hembery - who made no mention of the Barcelona test during the presscall - also admitted that producing suitable tyres would be a different challenge again, particularly as the company was still waiting for agreement on a new contract and had yet to receive any helpful data from the teams.