Tubelines, US project manager Bechtel's consortium with Jarvis and Amey, was named as preferred bidder to run the Jubilee, Northern and Piccadilly lines.
The announcement came despite a letter from Bob Kiley, London mayor Ken Livingstone's transport expert, to London Transport chief Sir Malcolm Bates.
In it, Kiley said LU's methods on evaluating the PPP bids were "illogical" and inconsistent. Given these shortcomings, Kiley said, it would be unwise to select preferred bidders at this stage.