BAR have slipped back after an impressive start to 2004

BAR have slipped back in recent races after a promising start to 2004.

"The crucial thing for us is to be seen not to have lost momentum and to carry that momentum into 2005," Willis told BBC Five Live.

"Our long-term goal to be championship contenders depends on us making steady progress from season to season."

Jenson Button finished fourth at the British Grand Prix, where it became apparent that the team were in danger of being left behind by the impressive new McLaren.

"This is a good test for us, and it's a test we need to pass," he said.

Willis said he was hopeful that delayed modifications to the car would be introduced for the German race next weekend.

"It's really important we introduce a number of mechanical, aerodynamic and engine upgrades that we've got and get them working on a car as soon as possible.

"I'd like to have introduced them earlier but for a number of reasons we didn't feel we'd fully tested them."