OBD 'disconnected'

Mods, please move this if it will be better answered in another forum.

I'm looking to buy a genuine VCDS for my 2006/7 Passat 140 (which I've had from new), but since its first French MoT in 2010 (it's 4 years before the first test is required in France), the tester has noted that they cannot check the OBD because it's not working. I asked at the VW dealer yesterday after its MoT, and they said it's turned off because of pollution, so that emissions have to be done at the exhaust.

So my question is, how can I turn it back on - and off again! Have they just popped a fuse out?