Despite the assurances of Pirelli, a number of drivers have expressed concern at two tyre failures on the first day of the Belgian Grand Prix weekend.

With failures thought to be a thing of the past in the wake of changes made by Pirelli following the numerous incidents that blighted the British Grand Prix weekend, failures to the right-rears on Sebastian Vettel's Red Bull and Fernando Alonso's Ferrari have put Pirelli back in the spotlight.

The Italian tyre manufacturer was quick to calm fears, insisting that the problems were caused by debris - though this is an excuse that has been used before.

"Towards the end of the afternoon session, both Sebastian Vettel and Fernando Alonso had a puncture on their right-rear tyre around turn 14 and we are currently investigating the cause," said Paul Hembery. "From initial analysis it appears that both were caused by an outside factor, probably debris on the track.”

"I don't think it's a similar problem to what we saw in Silverstone, maybe more of a random set of circumstances," said alonso, "but all the same it needs careful analysis."

However, Mark Webber, who heads to Sports Cars at the end of the season, was a little more sceptical. "We need answers. And 'debris' is not the answer," he told reporters.

"It looks on the Red Bull as though something has been rubbing on the surface and then has just cut through," said Hembery. "And on the Ferrari there are two quite clear holes through the top of the tread. So we have to go and look at the track later to see what is between turns 13 and 15."

Spa, and the forthcoming race at Monza, are two of the quickest circuits on the calendar, both circuits having seen more than their fair share of tragedies over the years. Consequently the drivers' concern is fully understandable.

"There is clearly something but I cannot tell you what it is," said Hembery. "It is from external sources. It is a worry for the sport because we have to go out and find what it is. We will try our very best to identify it and give us an indication of what is causing it."

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