I go to Harratts and find them very good. Spark plugs are about £60 a set, if you are handy with a spanner they are easy to do. Mine has just done 30,000 it had 15,000 when I got it. It has full Nissan service history but never had a P3. I asked again last year, they said they would see if it was necessary and just did another P2 instead.