I tried to get a spare key for my import as well recently, went to my local Nissan dealership, Ancaster Croydon, was quoted £498 for a spare key
The key has to be shipped over from Japan as I think the signal for the lock and immobilzer is on a different feqency to the UK spec key.
That still did not justify the price though, as I found out a spare key for a UK car was for around £250
Good luck and let me know if you have any success