is it a BUCHANAN? That body molded on a DB3S looks like it, in which case the mechanics are probably MG, or possibly HRG.
I haven't been able to ascertain the source of the body, but it could well be a Buchanan.
And the mechanicals are indeed MG, so that half-answers part of the question.
But that doesn't answer the puzzle, as I need to know the car's name, who built it, when and which MG it's based on!
Start digging...