You can't sue so that's not true. No vendor is obliged to even serve you in the first place - it's at their discretion. Even if you've eaten in a restaurant and then owe the money, they can refuse Scotch notes if they're not happy with them.
Notes (Scottish or English) are so widely available that they're an accepted form of exchange but merchants aren't legally obliged to accept them.
From memory, the only legal tender notes in Scotland were ones issued by the Bank of England and less than �5 so following their withdrawal of the �1 note, there are no legal tender banknotes in Scotland.