Despite speculation to the contrary, the Lotus Renault F1 team is sticking by its claim that a longer-than-expected pit-stop was to blame for the spectacular fire that put Nick Heidfeld out of the Hungarian Grand Prix.

The German was trying to make his way through the field after a poor qualifying performance that saw both black-and-gold machines miss the top ten pole position shoot-out on Saturday afternoon, but got only as far as his second pit-stop before being forced to retire with his car ablaze. The Enstone-based team had fitted the more durable prime Pirelli tyre at the stop, potentially giving 'Quick Nick' a shot at breaking into the points, but insists that a sticky wheel nut caused a crucial delay in the process which, in turn, led to the #9 machine catching light even before it pulled away from its stall.

"Nick had a very poor start and struggled in the wet conditions [but], in his second pit-stop, we had a problem with one of the wheel nuts, meaning that the car was sat at high revs for a long time," chief race engineer Alan Permane confirmed, "This meant a build-up of heat which caused a fire. Although it looked spectacular, it was only a small part of bodywork which burnt on the left-hand sidepod."

Although Heidfeld pulled away from his stop with the car already ablaze, he was forced to park several hundred yards along the main straight, before a minor explosion scattered parts across the pit-lane exit and left a fire marshal with minor injuries after being caught in the blast.

"My second stop was longer than expected and the car overheated," the German recalled, "I noticed smoke coming from the rear, it worsened, and then I noticed the flames, so I had to pull over at the end of the pit-lane and cut my race short. The last couple of races have not been what I hoped for, but we have a few weeks now to reassess and come back stronger after the August break."

Ricardo Penteado, the team's engine support leader from Renault Sport F1, insisted that Heidfeld's retirement was not due to an engine problem, even if the television pictures suggested otherwise.

"The Hungaroring is not the most demanding on the engines, so we used an engine on the fourth race of its lifecycle for Nick and on the third race for Vitaly [Petrov]," he revealed, "Nick's race obviously ended spectacularly, but it was not related to the engine."

With Petrov finishing only twelfth, Lotus Renault heads into the summer break on the back of its worst result of the year, and the first race at which it has failed to score even a single point. The Russian, like Lewis Hamilton and Mark Webber, was caught out by the brief shower which hit the Hungaroring in the closing stages, pitting for another set of intermediates before realising his error.

"It was a very difficult race, with very changeable weather conditions," Petrov confirmed, "When the rain returned near the end of the race, I lost temperature in my tyres and this made the car's handling very difficult. It looked like the wet conditions would continue, so I changed to the intermediates, but it did not last as long as we thought.

"Maybe we should have changed to the super softs, but it is so difficult to predict the weather, and many other teams did the same thing. I am a little disappointed as it was possible to score points had we done the perfect strategy, but it was not to be today."