I can help the Bank of England

The Bank of England might have “its own Bitcoin-style digital currency” this year already, according to the country’s legacy media. The more than three hundred year old bank set up a research unit back in 2015 to investigate linking a state-backed crypto to sterling, and there appears to be a breakthrough.

For the argument, let us define two way coin clearing is the blockchain, no third party.  Three way is the  current BofA, digital system; both digital.

Do a finite block chain coin with the BofA in charge of delete. So, you take your normal British three way digits, put them on reserve, and check out two way digits on the blockchain, valid for a thousand transactions. After a thousand transactions, the BoE freezes the blockchain and deletes accounts returning the balances to their normal three way banking system.

Then the bank has this simple robot escrow service, capable of executing protocols over long sequences, able to keep their regulatory balances, alter loans/deposits, execute ledger services externally.  The blockchain never gets steeper than the flow of BofE external transactions.  All the other central banks can create their own short block chains, anonymous, and work as each other's miners.  Then the central banks can, individually, call a timeout freeze on the escrows in process, clear our coin  hoarders.

It is not your three color central banking pit, buty a good step in that direction.