Took a quick picture of the exhaust - is this OEM or Milltek?
I gave the arm on the heater box a wiggle this evening. I now get slightly warm air coming through! Turning the arm a little further also seems to have stopped the breeze which was coming in across my legs so the car is now quite comfortable if you're wearing a coat. At the weekend I'll get the box out and seal it up. I think someone has changed the heater tube already as it isn't the OEM one.
Looks like I have a co-driver: