This particular Bassett-Lowke model is rather special, in that, although the model was in the company catalogues for some years, and is/was highly desirable, the high cost of the model combined with the fact that the LNER changed the default livery for new A4s after only perhaps a year or two, meant that very few were ever sold.
Bassett-Lowke only seems to have ever made a single batch of six of these models, and this example is the very first of the batch (number 1 of 6). This probably makes this particular model the first commercial (i.e. not special-order) gauge 0 streamliner model produced by or for Bassett-Lowke.