I kept noticing a damp patch on the floor under my exhaust, the only thing was it was the opposite side to the pipe, so I checked underneath and saw this. That is water leaking from the seams of the exhaust. The car is 2 months old, 1.6tdi SportBack. Done just over 2000 miles. It has been back to the dealer, they are ordering a new back box, should take a few weeks to come from Germany, they have been very good though. Hopefully it's a one off.