a very small fraction of a country’s total money supply is typically in the form of notes and coins. In the UK, this percentage is 2.1% of the 2.2 trillion GBP total money supply [@richard2011economics]. This then motivates the discussion of electronic money, or e-money, defined by [@al2009development] as a floating claim on a private bank or other financial institution that is not linked to any particular account. Under this rather general definition one can consider many different forms of e-money such as bank deposits, electronic fund transfers, direct deposits, and payment processors (including micro-payments).

Instead we put forward the rather more narrow definition of the UK regulator defines electronic money as follows (see @halpin2009developments):

“*Electronic money (e-money) is electronically (including magnetically) stored monetary value, represented by a claim on the issuer, which is issued on receipt of funds for the purpose of making payment transactions, and which is accepted by a person other than the electronic money issuer. Types of e-money include pre-paid cards and electronic pre-paid accounts for use online.*”

Typically, e-money is stored in the same unit of account as the fiat denomination used to obtain the e-money.

Cryptographically secure e-money
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In the case of early 