I have no problem with that, I believe the closest to the original 18th Century English is in Nova Scotia which is close to 18th Century Cornish (I seem to remember). .
English has always changed rapidly, that is a strength of the Language, however that is not the issue here.
The issue is that in England, the English are referred to as English and sometimes as British but never as British-English. It does not seem unreasonable to be able to call your own language by its name withou an externally enforced label.
We don't distinguish French as spoken in France (as opposed to Canada or various African nations) be referring to it is "Francais Francais". It is just Francais because that is what they speak in France.