Took the car in yesterday and guess what, they said they couldn't find anything wrong. Anyway, when they weren't able to answer my question as to where has all the oil gone then, they contacted Nissan GB.
The current situation is they have topped the oil up to the max mark and I have to cover a 1000 miles, go back in and they are going to dip the oil and report back to Nissan as to how much it's used. I will let you know what happens when I go back.