That looks like a Thorn fork to me, I know a couple of people who have the same model. The twin plate crown came later. The thing that gives them away is the mudguard fitting on the back of the fork between the dropout and the low rider boss, no other manufacture does this, or none that I've noticed.
There's a blog with some photos here
https://www.seasurfdirt.com/2010/09/24/nomad-mk1-a-big-lump-of-bicycle/Whether the bike is a Nomad, I wouldn't know. Maybe John will tell you the differences rather than just that it isn't. Apart from what it says on it, which might or might not be original.
My understanding of the EXP is that it was a beefed up version, I've only seen two and they had very distinctive X brake bridges on the seat stays, though I wouldn't know if they all had. Whether you'd want such an expedition machine depends on your usage, and to an extent your weight and riding style. Was the geometry different? It might be possible to tell that from later brochures.
EDIT - Some photos of the various models in this thread
http://thorncyclesforum.co.uk/index.php?topic=11607.msg84501#msg84501