John Adrian Shepherd-Barron’s was letting off steam while sitting in steam.

It was 1965 and bank kept strict business hours. Shepherd-Barron had failed to get to his branch on time to withdraw the money he needed, so still fuming he had returned home and decided to take a bath.

Ensconced in his tub, like Archimedes he had a “eureka” moment. “It struck me there must be a way I could get my own money, anywhere in the world or the UK. I hit upon the idea of a chocolate bar dispenser, but replacing chocolate with cash.”

Luckily for him, his work at De La Rue Instruments provided him with an opportunity to meet the then chief general manager of Barclays Bank. He grabbed the opportunity to pitch his idea: “If you put your standard Barclays cheque through a slot in the side of the bank, it [the cash machine] will deliver standard amounts of money around the clock.”

A contract was quickly drawn up and signed, over a pink gin according to some versions of the story. It wouldn’t however be till 1967 the first ATM would be installed at a Barclays branch in the north London suburb of Enfield.

Reg Varney, from the successful television series ‘On the Buses’, was hired as the celebrity to be the first person to withdraw cash.

The machines worked with cheques, Each cheque had to be impregnated with a mildly radioactive chemical – fortunately it was one that was harmless to humans. The cheques were also encoded with a personal identification number (PIN) that the user had to key in.

It was Shepherd-Barron’s wife who suggested that a four-digit code should be used as she thought that six figures would be too many for most people to remember.

The first machines paid out only £10 but as Shepherd-Barron observed that, at that time, this was “quite enough for a wild weekend.”