I have put together a spreadsheet of probable early UK MX5s. Something very odd happened with the registrations at the time.
G174 RKM remains the oldest UK MX5 (though it was probably a Eunos Roadster fitted with UK-spec parts), registered 17 January 1990, with the DVLA mistakingly putting the engine size down as 1498cc.
Liz Turner’s book includes a photograph of a white 1990 UK car, with a stick on plate, with the photograph being indicated as taken on Greece as part of a press launch. The registration of this car is G215RKM. Can anybody confirm whether this press launch actually took place? If it did, I assumed Mazda probably arranged for a collection of cars, in different colours, to be available to the journalists. Does anyone know if these cars had stick on plates fitted (fitted I would assume, if true, because the UK spec number plate brackets were not available)
G215RKM is listed as being registered on 1st February 1990, bizarrely the day before G175RKM. I always thought registration numbers were issued in sequence.
A bit of poking around reveals a series of Mazda 1597cc cars, all being registered on 01/02/90, from G201RKM to G216RKM, 4 blue cars, 4 red cars, 3 white cars and 4 silver cars. G200RKM is a 1597cc Mazda of some sort but its in black, and G218RKM is a 1597cc Mazda in yellow. In principle, these cars might have been 323s with the same B6 engine, but many of these cars are still taxed, which would conspire against them being 323 (the vast majority of these 20 year old Japanese hatchbacks will be in cubes by now). The yellow car is now toast, but I do recall an early UK car that came from Mazda France in yellow (but left the factory in red); I couldn’t find a trace of red on that car, and the story was that Mazda might have used it for photography purposes (it had an odd mix of UK and Japan-specific features). The black “MX5” is still about. One of the series apparently had a very short life; being last taxed in August 1990; I suppose its possible that it was put on a private plate, but it would be pretty remarkable for a 21 year old car still to retain a private mark (when the marks are transferred, I though the original issued plate is reissued to the car). The cars have been registered in blocks of colour, so the vVINs might be in order (ie. G201RKM is an older car than G216RKM, by about 3 hours).
The contender for the oldest “proper” UK MX5 surviving is between G175RKM, a mariner blue car, registered on 02/02/90, G201RKM, also in Gods own colour, registered on 01/02/90. The mystery black car, G200RKM was registered 02/02/90 (yes, strange that). Both of these cars are still listed as being taxed. The 01/02/90 cars were registered in the following order (first to last): blue, white, red, silver. I suppose it might be possible that other MX5s were registered on the same day in different areas (“KM” indicates a Maidstone/Kent registration, which coincides with MCL’s address). Need someone to confirm from the chassis numbers, and also if the odd painted cars were MX5s, delivered in those colours, or later repaints, or some other small engined Mazda. Out of 17 01/02/90 registrants, 9 are still taxed.
The oldest car in the UK badged as a MX5 from the factory though is a very early 1989 Australian car that surfaced in Northern Ireland (imported in 1991). It looks more or less the same as a Roadster, with a small opening for the rear plate.
G177RKM, the Autocar cover car, was last taxed (and presumably scrapped) in 2004 
. RIP.
I have also collected together other registrations of MX5s appearing in the national literature, into a spreadsheet that I’m happy to share, if anyone wants to find out if their car was once the “star”. I won’t publish the list here, as although it includes some of the Mazda press cars (used in promotional literature, or loaned to magazines), it also includes cars provided by owners for magazine articles, and these owners, for whatever reason, might not want this broadcast. But, it included 2 cars well known to me, but not seen for about 10 years, that have survived. The list isn’t comprehensive, as its just based on the literature I have, listing 69 MX5s and Roadsters.