I was speaking to my car dealer mate (regular visiter to Edinburgh DVLA office) and he was explaining to me why at the moment all the new cars registered in the Edinburgh, Lothian, Borders and Central areas are getting reg prefix 'TN' as apposed to a Scottish plate such as 'SK, SL, SM, SN' etc.
He was saying that Edinburgh office has had such a demand on lately and they have staff shortages as well as the fact that they are just slow resulting in new car reg requests having to go to the Carlisle office.