Many thanks for your comments guys! I think I will have it fixed under warranty and then use the option to switch if it becomes a pain in the nether regions.
Recently purchased 320d Luxury - ex demo with low mileage. As I understand it engine should cut out when stationery - lights etc. Been to dealer once and they want to have it for a whole day for investigation. Any ideas what could be wrong? Also, if it works is it a good thing or will it become a pain? Any views welcome.