You need a banking licence from the government to start a bank.All through this thread you keep pointing out that cash isn't free at the same time implying that cashless transactions are somehow not paid for by the customer. You're wrong.
I gather from earlier posts you run your own business so I would imagine you may over the years have taken out loans from the banks. Where do you think that money came from? It's backed by the funds that the banks hold from customers in credit. The money you put in a bank doesn't sit there doing nothing.
It's basic economics, a labourer is paid for his work. He turns his efforts into money.
A bank loans out money and charges interest, the interest is how they make the money work for them and on the strength of having liquid assets they can lend the same sum several times. So the bank may have £1 million in funds from accounts in credit but they can lend many times that amount and collect the interest on it. As long as people leave their money in the bank all is fine. Remember what happened when Northern Rock went tits up and everyone wanted their money in hard cash not notes of credit.
To put it another way if banks make no money out of accounts in credit why don't you start a bank with nothing but accounts in debt and see how that plays out.
The reason being that this is a licence to create currency. They aren't issued very often.
The assets of a bank mostly compromise its mortgage loans. So by extension, a bank's assets are the real estate the customers have borrowed against.
The downside to this banking licence, is that the bank effectively becomes a utility, controlled by the the government and pressurised in all sorts of ways to carry out unprofitable activities. For example, maintaining High Street branches, providing accounts to dodgy unreliable customers, just because they happen to be UK citizens, etc.
HSBC has recently been told by the UK government not to pay out dividends. Much to the annoyance of its shareholders in Hong Kong.