Lotus denies Kimi Raikkonen has lost interest after Ferrari deal

Raikkonen has been outqualified by team-mate Romain Grosjean at every race since he announced ahead of the Singapore Grand Prix that he was rejoining Ferrari in 2014.

But Boullier is adamant that Raikkonen's form has nothing to do with him losing motivation. Instead he thinks Grosjean having stepped up his performance is the major factor.

When asked by AUTOSPORT if he felt Raikkonen's interest had waned now that he was leaving Lotus, Boullier said: "Not at all. I don't think so.

"I think it is more about Romain, who came back in the game. If you remember last year, Romain was very much up to speed but, if I may say this, then his spirit went down and he lost ground a little bit. But Romain is now back."

Raikkonen's performances have also been hampered by the fact that he does not like the new Pirelli tyres that were introduced from the Hungarian Grand Prix.

LONG WHEELBASE GAMBLE PAYS OFF

Lotus has emerged at Red Bull's main challenger in recent races, and Grosjean even led the early stages of the Japanese Grand Prix.

Boullier is proud that his team's recent efforts have so clearly paid off.

"What we brought during the season delivered the performance expected," he said.

"It is true it was a bit of a gamble, but I am proud of what we could achieve with the long wheelbase package - which is not only about the wheelbase but also the aero around it.

"It is good to see that the new processes we put in place, including the driver in the loop simulator, look like they work.

"It is good to see that we could raise our game a little bit to improve the car in qualifying and keep the characteristics of the car for the race."