I'm a complete novice at posting on here and thought that this reply would position itself under David's post. Apologies for messing up the chain.
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You're absolutely right in the literal sense in that being the first development car for the production Rover spec (at least that's what I was told via the forum a while ago) it is a converted MG ZT, I view it as ending up as a Rover after the company's work. Its starting point as logged by production data would be its MG ZT 260SE origin, and DVLA have that too.