Utopia, you are standing in it!

Since 1844, the Bank of Scotland, Clydesdale Bank and The Royal Bank of Scotland have been allowed to issue banknotes in denominations of £5, £10, £20, £50 and £100.  Only the Royal Bank of Scotland continues to issue a small volume of £1 notes. Two Northern Irish banks have similar prerogatives.

These Scottish banknotes are not legal tender in England. No banknotes have legal tender status in Scotland, whether issued by Scottish banks or the Bank of England. The Bank of England says:

Scottish and Northern Ireland banknotes are fully backed at all times by ring-fenced backing assets partly held in Bank of England notes and UK coin, and partly as balances on accounts maintained by the issuing banks at the Bank of England.

Consequently, holders of genuine Scottish and Northern Ireland banknotes have the same level of protection as that available to holders of genuine Bank of England notes.

The acceptability of any means of payment, including banknotes, is essentially a matter for agreement between the parties involved in a transaction in Scotland.

Bank of England keeps control Scottish bank notes in issue by stipulating that the issuing bank hold in their reserves the same amount of UK money (either in cash or on deposit at the Bank of England) as the Scottish notes they issue. These reserves could easily be converted to a currency board.

• A currency board issues local notes and coins anchored to a foreign currency (e.g. Sterling) backed by government bonds with 1 pound sterling  pound sterling and British government bonds for every Scottish pound currency note issued.
• A currency board issues domestic notes and coins only when there are foreign-exchange reserves to back it. In the case of a Scottish currency board, there would be pounds Sterling reserves to back any Scottish pounds and currency notes on issue.

The Hong Kong currency board has operated successfully through 30 years of financial turbulence and radical constitutional change. There is no reason why a Scottish currency board could not do likewise, guaranteeing the convertibility of a Scots pound, initially at parity with the English pound sterling.

After independence, Ireland acted effectively as a currency board until the 1970s. Currency boards were commonplace throughout the British Empire and were highly successful.

• On the independence of the Irish Free State in 1922, the introduction of an independent currency was a low priority because 98% of exports and 80% of imports were with the UK.
• British banknotes and notes issued by Irish banks circulated (but only the first were legal tender) and coins remained in circulation.

Under the Currency Act 1927, the Saorstát Pound (Free State Pound) was created at parity with the British Pound Sterling. A Currency Commission kept British government securities, sterling cash, and gold to keep a 1:1 relationship between the two currencies.

Although a Central Bank of Ireland was created in 1943, the Irish punt remained linked to sterling with the central bank operated as a de facto currency board policy until joining the European Exchange Rate Mechanism in 1979.

A currency board has no capacity to act as a lender of last resort to a Scottish banking system.