Following Ramp's very helpful reply, I did some checking. It seems that any M-B dealer can produce the report if you supply the VIN. When you think about it, I suppose the system allows M-B to check that a vehicle has a proper service history so that it qualifies for warranty repairs, but it also provides protection for a vehicle buyer. I suspect that if the existence of VMI was more widely known all purchasers of used M-Bs would insist on seeing a report.

When I used Google to get more information on NetStar VMI, all of the search results pointed to sites in the USA, so I'm not entirely confident that the facility is available here in the UK. I'm going to check this out with a dealer, but if in the meantime anyone has better information that would be appreciated.