Mercedes have rubbished claims Pirelli have handed the world champions a critical performance advantage by changing their tyres mid-season.

Pirelli have amended their tyres by reducing the amount of tread on the compounds for this weekend's Spanish GP as well as the upcoming races in Britain and France.

On Thursday, Sebastian Vettel said: "Obviously we have different tyres because Pirelli reacted to the issues Mercedes had and Red Bull had in testing."

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When asked if Pirelli had altered the tyres 'to help Mercedes' after he took pole position for this afternoon's race, an unimpressed Hamilton responded: "That was a stupid question really, so I don't really have an answer for it."

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Although Mercedes are believed to have suggested the tyres were altered after suffering from overheating in winter testing at Barcelona, Pirelli say they took the decision independently.

"Is b******ks a bad word in English?" responded Mercedes boss Toto Wolff when told the Silver Arrows' rivals had complained.

"It is rubbish. All the teams had very heavy blistering in testing - Red Bull, Ferrari and ourselves. The tyres wouldn't have lasted in the race and the ambience and track temperature was arctic [in winter testing]. For that reason, Pirelli changed the thickness of the tyres to prevent the blistering, and they have been successful because we haven't seen any blistering today.

"I don't know where this rumour has come out from that we have been influencing Pirelli and the FIA. I've never seen anything like it. Why would they do it?"

When's the Spanish GP on Sky?

The Spanish GP is exclusively live on Sky Sports F1 - Saturday Qualifying underway at 2pm, lights out 2.10pm on Sunday.

Wolff continued: "In the past, when we have not performed we have taken ourselves by the nose and looked to find performance on our car. We didn't have a default mode of asking what are the others doing that was wrong."

Red Bull's Max Verstappen was equally dismissive of the claims, stressing that only 0.4mm of tread had been shaved off and adding: "On this track in testing you could see the supersofts weren't behaving as well as the softs."

But Ferrari's Kimi Raikkonen said: "Sometimes it works for one team better than others. It's pretty difficult to say how different it would have been had we had normal tyres."

According to Raikkonen, the change is particularly apparent on the supersoft tyre - the compound which Ferrari abandoned for their final runs in Q3 despite the soft tyres theoretically possessing less grip.

Mercedes have struggled to master the 2018 Pirelli tyres all season and Hamilton's pole position at Barcelona was his and the team's first since the season-opening Australian GP.

But with Mercedes also tending to perform especially strongly in cooler climates, Wolff isn't yet convinced the team have found all the answers to their Pirelli problem.

"It's very complex to understand," Wolff said. "This is a track where we were quick in winter testing, which has been resurfaced and the ambience is cold. So you could say that it suited us.

"We have had races where we weren't as competitive as we wished so there is an additional set of data we can look at and try to filter what is important and what is not."

Sunday's race, exclusively live on Sky Sports, starts at 2.10pm.

Ahead of the Spanish Grand Prix, watch Martin Brundle's alternative gridwalk on the city street of Barcelona.

Will Lewis Hamilton and Mercedes make it back-to-back victories at the Circuit de Catalunya? Watch the Spanish GP exclusively live on Sky Sports F1 from May 11-13. Get Sky Sports F1.