Fraser made a post about the police view
http://forums.sv650.org/viewtopic.php?t=20876
I think you're out of luck on the numberplate issue, but I think your garage is right about the exhaust; the BS/EU stamp is not a requirement, as such.
It's all a bit complicated really, and the construction and use regulations are different to the MOT regs.
I won't give my interpretation of them, here, though, that would just confuse matters further, I think.