I have found a picture of this car in an obituary of the recently deceased Spanish driver José Miguel García "Morisco". The article says that he raced two barchetta-type cars: a Lucchini P3, which looks very different to this, and a "McLaren Mk8", which I'm not sure what is supposed to be, so could that be this car?
That is the answer I'm looking for, and the point is yours.
I found this car for sale in the Canary Islands. It was being sold as an Elva McLaren MkVIII, supposedly chassis no. 80003, one of 5 built. The seller claims it was built for John Nicholson of McLaren Racing (sic). It's powered by a BMW M3 engine and I reckon it was used for hillclimbs.
What is it? I have no idea, but I think it has no connection with McLaren whatsoever, and possibly that company's name was being used to make the car seem more interesting. I think it's an Elva MkVIII which has been rebodied in a more modern style. Just a guess. Elva were only involved with McLaren when they built the Mk2A CanAm cars at the Trojan works IIRC, which were known in the States as the Mk1. McLaren had nothing whatsoever to do with the MkVIII.
If you have any more information. please post it here.