There is also the prospect of using FlyBuys-style cards. Turnbull cites one of Australia's largest loyalty programmes, which has more than 9mn members. It allows members to accumulate points and then use these at a variety of stores.
According to latest statistics, 15 Flybuys are scanned every second on average in Australia.
Turnbull says these sort of digital credit cards could be issued by "supermarkets, city and regional councils" and used by customers for future purchases, taking the idea of store loyalty cards that one step further and widening the potential scope.
Andy Haldane, former chief executive of the Bank of England and now chief executive of the Royal Society of Arts, told FT Adviser: "We can of course create private sector alternatives to central bank money.
"In essence, some of the cryptocurrencies that are proliferating are seen to do some of those things. But ultimately what matters most about any kind of money is trust in that money.
"The benefit, what is impossible to replicate in the private sector, is that central bank money is backed by the government, by future taxpayers.
"So of course we might use central bank money more sparingly, but do we think it can be replicated in its functions by something private sector in origin? I would say 'not on your Nelly'. That won't happen in my lifetime, nor in anyone else's."
Who could create such a currency?
Turnbull points to the wider business world for possible solutions as to who could create a lifeboat currency.
Building societies and mutuals could take some note of the US credit union model, which was given the green light to partner with cryptocurrency providers. But the regulatory hurdles might prove too high to overcome in other countries, such as the UK, which is barely showing amber lights to crypto.
Turnbull says: "The most likely organisations to introduce digital lifeboats are large retail store and digital businesses that provide digital loyalty points to promoted sales.
"They could create an option for customers to make their digital promotional credits redeemable at any other businesses. This would include The City of London rates, and so on.
"Also it could also replace Transport for London's Oyster cards that people could use each day to amortise its negative interest rate. This option would require the card to lose, say 2 per cent of its value each week while the card remained in circulation, until it was redeemed for cash after 52 weeks by the issuer.
"The issuer would earn 4 per cent more than the initial value of the credit provided. Such a card could be used as cash money at any shop with a card reader to confirm its residual value."
