There is. And it is quicker. As you arrive at the lift area from the walkway from the station, carry on and go down the short escalator in front of you, rather than turning left to the lifts. You are now in the check-in area of T1. Turn left and there are lifts ahead of you at the end of the check-in hall. Take the lift to the ground floor (I think marked 1!) and that takes you to the outside area between T1 and T3. This way is quicker as the lifts aren't much used.