UPDATE:
Went down to the stealership and the service manager looked at the car. He had the wheel off and spoke with his technicians etc.
To cut a long story short...he agrees with me that the scratch was most likely not there when i brought it to them and agrees with me that it was there when i called him 25mins later when i got home. Therefore he reckons it happened on my way home (about 5 miles in rush hours traffic therefore very slow pace) by a stone or something getting caught between the wheel and caliper. What a load of toss - it is almost laughable so i wasnt very haoppy and made him aware of this!
He said that he will look around for a quote to get it refurbished (not that he even would accept liability but suggested he may put some towards it, though would not commit to a figure ££). He rang me today saying that he couldnt find anyone who could match the brembo paint. Had no luck directly from nissan, they were trying to get him to buy a new caliper, on back-order, at £1200 each . So now he is waiting for Brembo in Itlay to get back to him with a paint code.
Just get the feeling he is trying to fob me off but is there feck all i can do about it??? I aint happy.