McLaren's managing director Jonathan Neale said the team's sole aim was to win both world championships due to the driver talent at its disposal.
Behind the scenes at the McLaren launch
Behind the scenes at the McLaren F1 launch, part two
However, Whitmarsh held off from saying the car would be good enough to help Button defend his world crown, or Hamilton regain it.
"Is it a championship contender? It's still far too early to say," he said. "Will it win races? We certainly hope so. Am I proud of the effort we've currently invested in the car? Most definitely."
Jenson Button said he was already felt an integrated part of the team.
"In my brief time here I feel I've become part of the team," he said. "I really sense the start of the last year makes McLaren hungrier for success this year.
"I've spent a lot of time in the simulator which has allowed me to work with my engineers. This is the hardest part of my change, getting to know my new colleagues."
Lewis Hamilton said the team had been very accommodating towards Button and he was looking forward to competing against him.
"We've been very welcoming to Jenson," he said. "I've spent some time working on the car now and am proud of my input on it. Hopefully we can add some more input and have a great year."
Whitmarsh also praised his all-British driver line-up.
"I'm relatively relaxed about the driver partnership. Knowing Lewis as I do, and having got to know more of Jenson during the limited time I've spent with him during his busy visits to MTC, I feel relatively confident that our driver line-up this year will be a very stable and mutually productive one," he said.
"Neither became world champion simply by driving at the limit on the racetrack; they've each been responsible for moulding and developing an organisation around them, and in exploiting the skills of their respective engineers to the best of their abilities.
"And it's that sort of approach that we'll be looking to encourage from both drivers in order to give us a performance advantage.
"Of course, we wouldn't be going racing if we couldn't let our drivers 'off the leash', but our absolute priority is to develop a front-running car."
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