Thanks @Rikz2004, done all that and it all appears fine, I even cleaned the MAF and it made no difference. However, I think the MAF may be faulty. When the light came back on again I plugged the OBD reader and cleared it again, checked a few parameters and watched the intake temps. They were around 45 and crept up to 51 and stayed there for a while before leaping to 205!! So I assume there is some kind of fault with it.
Anyone know where's best to get a new one? No interest in eBay copies, or paying £200 to Nissan lol