Mat Coch writes:

A piece of tungsten found in a kerb is to blame for the punctures experienced by Sebastian Vettel and Fernando Alonso during second practice on Friday, says Pirelli.

In the closing stages of the session Vettel was seen limping back to the pits with a punctured right-rear tyre, a fate which had also befallen Alonso seconds earlier.

With tensions running high following the dramatic British Grand Prix weekend questions were soon being asked of Pirelli, which immediately investigated the incidents.

"The first evidence and the most important evidence for us was telemetry data coming from Ferrari," Pirelli's Motorsport Director Paul Hembery told Pitpass. "They noted in turn 13 a slow puncture occurring so they asked Fernando to slow down and he came into the pit lane.

"We could see two holes in the top of the tyre - like a vampire bite - two fang marks on the top of the tyre," Hembery continued. "Analysing the tyre you could see that one of those had penetrated to the inside of the tyre and that was the cause of the slow puncture."

Following the session the Italian company investigated the circuit with FIA Race Director Charlie Whiting, specifically the middle sector of the lap. Upon inspection a piece of metal, which may have fallen off a car, was found.

"We found on the outside of Turn 13 a piece of metal, a piece of tungsten, a dense piece of material with two points in," explained Hembery. "Bringing that back to the tyre we could see the two points correspond with the two holes in the tyre of Fernando.

"We then saw that Vettel passed over the same point about 15 seconds after Fernando. Analysing the tyre we could see again the issue was coming from external sources and the holes in the tyre matched against the piece of metal that we found on the circuit.

"Both tyres we confirm are due to external sources and the piece of metal that came from a car.

"At the same time obviously for caution we analysed the cuts and verified internally a significant number of other tyres from both teams and other cars and there's certainly no indication at all of any fatigue issues.

Cuts found on tyres at Williams and Marussia are believed to be unrelated and are not a concern. "We saw some light cuts but nothing significant," Hembery said. "If you go and look at some of the kerbing here there are some little bits of concrete coming away. It's more lacerations rather than substantial cuts."

Mark Webber raised concerns regarding the tyres following yesterday's second practice session, suggesting that the 'debris' excuse had been worn out. Hembery however was unmoved, believing the Pirelli tyres fit for racing.

"The tyre's here are the same they've used for two years almost without issue," Hembery countered. "A piece of metal like that is going to be, to any circuit racing tyre, is going to be a massive challenge.

"If you've got a large piece of metal coming off there's very little you can do."