Thanks to all for the help. SD card now on order.

The head unit has a "Nav" button and a slot for an SD card. I'm including a picture here, as QashqaiSilver suggested:

Sorry to jump in with both feet. I've just got my first QashQai but my second Nissan (the first was an 80's Datsun Bluebird 180B). The car is a 2009 1.5 dCi n-tec and the entertainment unit looks suspiciously like a Connect 1 -- but shop.nissan.co.uk says that none of the stuff for any Nissan factor...