Surely with the impending feed in tariff we should be talking generation meters not export meters and to complicate there is night tariff .
Yes - as Ted says - the generation meter is important too. The difference though is that the generation meter is yours, whereas the import/export meter is 'theirs' (the network operator).
You fit your own generation meter, or at least your installers do, and so long as it's on the accredited list, then it should satisfy OFGEM or the FITs people. If you had more than one generator, maybe different technologies, then you'd have more than one generation meter.
Whereas you have to get the DNO to arrange to fit an export meter (if you're on some export deal where it's relevant). Pleased to see that Ted's got import/export in the same meter - wish I had - anything that made for less meters and wires in my small cupboard. But you can't really have the generation meter as part of the same device, since it's a different pair of wires that's being measured.