Scottish Notes : Worth Paper If Bank Goes Kaput?

Scottish and Northern Irish note-issuing banks are required by British law to hold full face value in Bank of England notes in reserve, as backing for their own notes. This law is primarily in place to protect note-holders from suddenly finding their paper money worthless.

It should be noted that the famous "million pound notes" were printed specifically for this purpose.

So yes, even if the bank goes bust, you should still get full face value of the notes from the Bank of England.

The Isle of Man is a separate case; as an autonomous crown dependency, the Manx government itself, rather than the local banks, is responsible for maintaining the currency union with the mother country and for backing their notes. According to Wikipedia, while Manx notes aren't normally accepted in payment elsewhere in Britain, most banks will happily accept and exchange them for free.