you need to go to the dealers if you have a NATS system fitted. but the problem you have is getting it there lol. i would give your local nissan dealer for advice
don't expect it to be cheap though. They wanted something around £60 to re-program the key to the ECU, and then they won't come out to do it, you need to get the car to them, they said they'd get it for £40, then they wanted more money for another set of keys....