Glynis, hubby has just been up there, and thinks it would be awkward to get out of there without going through the barrier, especially if another car was behind. What they told him was that pick up/drop off is up to 10 mins free. You get your ticket at the barrier machine, then put it back in when the drop off is finished, less than 10 mins, no charge, over 10 mins £2.50, and no return within 30 mins.
We always put the car in the garage and get a taxi, so don't take much notice really.
I have just rung and booked the taxi for Wednesday, and they told me the same thing, 10 mins free.........