A furious Christian Horner has accused Mercedes and Pirelli of "underhanded tactics" before Sunday afternoon's Monaco Grand Prix.

Horner, the Red Bull team principal, has lodged an official complaint after reports emerged that Mercedes and Pirelli had conducted a tyre test at Barcelona's Circuit de Catalunya following the Spanish Grand Prix.

In-season testing is banned but it is understood that Pirelli can call upon one team for private help if they need it.

The testing is understood to have covered 1,000 kilometres and three days. What has incensed Red Bull, and Ferrari, is that they knew nothing about the Mercedes arrangement. And there is speculation here that the FIA, the sport's governing body, knew nothing of what had taken place.

Mercedes are currently the quickest car out there over a single lap, and the only reason that they have not been winning races is because of the trouble they have had with rear tyre degradation.

Horner said: “What annoys me is that it was so underhand. And it makes a mockery of the rules. We have just spent three hours in Bernie’s bus discussing eight days of pre-season testing for next year and it is already going on.

“We have protested it. I don’t now what Ferrari have done.”

At first there were rumours that Mercedes, who have locked out the front of the grid for today’s race, might be penalised and pushed back down the gird. But the matter is now likely to be addressed next month.

Pirelli have promised to change their too-vulnerable tyres before next month’s Canadian Grand Prix, and there will be a further fundamental change next year to take into account the fundamental changes to the engine.

Horner added: “First of all we need to deal with it through the proper channels, and that’s what we’ll look at doing. There is confusion between what is contractually permissible and what a team is allowed to do in the sporting regs.

“It’s a situation we need clarification on, and our position is we are going to request that clarification. I can understand Pirelli wanting to test the tyres, they’ve obviously got issues with the tyres.

“What’s disappointing is it’s been done in not a transparent manner, that a three-day test has taken place with a current car running on tyres that are going to be used at the next grand prix. Irrelevant of what you call it, that’s testing.”

Paul Hembery, Pirelli's motorsport director, said: "It's completely regular in that we are allowed to do a 1000-kilometre tyre test with any team. In the World Rally Championship contract it's exactly the same. We can do it with a representative car.

“We’ve done it before with another team, and we’ve asked another team to do some work as well. In reality, we were looking at next year’s solutions and trying a variety of different things.

“Mercedes haven’t a clue what on earth we were testing in reality.”

Asked about the prospect of Mercedes gaining the upper hand, Hembery added: “Absolutely not, no, because it’s no relevance to what’s happening here. The bottom line is we’ve been trying to find a way to test.”

Guardian Service