The Bank of England does not issue any notes greater than the £50 note. However, under laws introduced in the 17th Century, Scottish banks are allowed to issue their own banknotes. Three Scottish banks choose to do so:
Bank of Scotland
Royal Bank of Scotland
These banks issue notes in the same denominations as the Bank of England (5, 10, 20, 50), plus they issue £100 notes, the largest pound sterling notes issued. The notes' designs vary according to the bank which issued them, and even the lower denomination notes carry different designs to their Bank of England equivalents.
Oddly, these Scottish banknotes are not legal tender anywhere, even in Scotland. However, 'legal tender' is a very specific technical term, and has little to do with real-life day-to-day trading. Credit cards, for example, are not 'legal tender', but it's perfectly legal to use them to pay for things. Similarly, you can use Scottish notes in any part of Britain, although sometimes you might have a little trouble with cashiers outside Scotland simply not recognising the things.