Have you had anything replaced on the steering/front suspension recently? I only ask because my steering is slightly on the sqiff & I'm been told it's because that the garage I used to replace a track rod end only replaced the one instead of the pair... I think I got that right!:embarrest:
Also, jack the left front wheel up & check for play.
have you tried braking somewhere flat, like a car park to see if the cars still pulls to the left?