No it's not, Scottish bank notes aren't of a different currency - they're still pound sterling. The reason they're typically not accepted in English shops (at least, those not on the Scottish border) is most often because they're rather uncommon so it's more difficult for cashiers to detect fakes. My understanding is also that some banks, when depositing, require the English and Scottish notes to be separated and may charge a fee to convert them to English notes, so it's more effort to accept and handle them.