Scots banknotes are readily exchanged in English (and Welsh) banks at face value "quid pro quo!". But are, nonetheless, not 'legal tender'. And although many Scotsmen (and some bankers) will tell you otherwise, they are not 'legal tender' in Scotland either.
But they are generally accepted, and most businesses in the rest of Britain will also accept them, as they know they can just pay them into their own bank with the takings.