That's how GM built them- fuel filler on the left hand side. Very doubtful they would have changed that for export (RHD) models. In addition to the U.K. exports, it could also have been imported into Australia at some point in the past- at one time not too long ago all LHD vehicles brought into OZ were required to be converted to RHD.
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Heck, it could be a U.S. rural postal delivery car! :lol: Express Mail!