It seems to me the way the UK went about this was not very efficient. Australia had changed from a nearly identical £/s/d coinage to its own decimal system five years earlier, with less wastage, by changing the name of its currency from pounds to dollars. This let them renumber the paper banknotes.
First the Australian scheme, because it was simpler. There were copper coins for 1d, 2d, 1/2d, and silver coins for 3d, 6d, shilling (= 12d, written 1/-), florin (=2s, written 2/-), and crown (5/-). The banknotes were 10/-, £1 and up. The elegant solution was to set £1 = $2. Then the silver coins, except for the 3d and the crown, could all be retained: the sixpence became the 5c piece, the shilling 10c, and the florin 20c. And relative to the 10/- (now $1) note, they were all still their usefully-sized selves. The crown was withdrawn – I think they wanted to anyway, perhaps because of a counterfeiting problem – and replaced by an incompatible 50c several years later. The copper coins were replaced by new 1c and 2c coins. New silver 5c, 10c and 20c coins were minted, the same size and weight as the old (so they could be used in vending machines) and replaced the old silver ones gradually. The banknotes were all replaced immediately, but as they were paper back then, banknotes got soiled quickly and replaced often anyway, and the opportunity was taken to design new ones that were better for the visually impaired.
However, the British kept the £, which meant the shilling would have to be 5 of the 1/100th units. The British pre-decimal coinage was similar to the Australian, with addition of the farthing, which was 1/4d. But now 6d = 2 1/2p so that, as well as the half crown and all the coppers, were useless, and the shilling was stupidly large for 5p. I guess it's a matter of opinion as to whether 25p should have been a thing, but units of 5c and 10c make more sense to me.
Australia was now also able to change its typewriter layout from the UK one to the US one, as £ was no longer required. In the meantime, $ could be produced by overstriking S and I.
It was also later recognised as a mistake because it added an inflationary boost just as the Oil Shock triggered even higher inflation.
A better solution would have been to contine to allow inflation to "decimalise" the currency. Lower value coins (e.g the farthing "quarter penny" a few years earlier) were being removed.
When it came time to withdraw the old penny it would have left the thruppence (3 pence) as the smallest coin, worth a quarter of a shilling. Replace that coin with a new penny worth a fifth of a shilling and decimalisation has occurred naturally.
No mention of the Guinea (21 shillings) that was the unit used to quote professional fees (lawyers, doctors) and exclusive stuff such as custom clothing. I think race horses are still sold in Guineas, which are now 1.05 pounds.
To avoid bringing down the whole pile of absurdities, like some numismatic tower of Babel..
I was five when this happened, and still remember grown-ups complaining bitterly. The old coins did have a certain weight to them, both historic and physically. When the pound coin was introduced people complained again. The strangest thing to me was the difference in size of the bank notes - £20 was flamboyantly larger than the pedestrian £1 note, it seemed huge.
Your comment spurred me to find the Wikipedia pages about notes. I had always been aware of the gradual shrinking of the dimensions, but didn't realise it happened so dramatically from pre-war to 70s [1].
Huge notes always remind me of Bresson's Pickpocket - a decade earlier but close enough [2].
Readit News
First the Australian scheme, because it was simpler. There were copper coins for 1d, 2d, 1/2d, and silver coins for 3d, 6d, shilling (= 12d, written 1/-), florin (=2s, written 2/-), and crown (5/-). The banknotes were 10/-, £1 and up. The elegant solution was to set £1 = $2. Then the silver coins, except for the 3d and the crown, could all be retained: the sixpence became the 5c piece, the shilling 10c, and the florin 20c. And relative to the 10/- (now $1) note, they were all still their usefully-sized selves. The crown was withdrawn – I think they wanted to anyway, perhaps because of a counterfeiting problem – and replaced by an incompatible 50c several years later. The copper coins were replaced by new 1c and 2c coins. New silver 5c, 10c and 20c coins were minted, the same size and weight as the old (so they could be used in vending machines) and replaced the old silver ones gradually. The banknotes were all replaced immediately, but as they were paper back then, banknotes got soiled quickly and replaced often anyway, and the opportunity was taken to design new ones that were better for the visually impaired.
However, the British kept the £, which meant the shilling would have to be 5 of the 1/100th units. The British pre-decimal coinage was similar to the Australian, with addition of the farthing, which was 1/4d. But now 6d = 2 1/2p so that, as well as the half crown and all the coppers, were useless, and the shilling was stupidly large for 5p. I guess it's a matter of opinion as to whether 25p should have been a thing, but units of 5c and 10c make more sense to me.
Australia was now also able to change its typewriter layout from the UK one to the US one, as £ was no longer required. In the meantime, $ could be produced by overstriking S and I.
A better solution would have been to contine to allow inflation to "decimalise" the currency. Lower value coins (e.g the farthing "quarter penny" a few years earlier) were being removed.
When it came time to withdraw the old penny it would have left the thruppence (3 pence) as the smallest coin, worth a quarter of a shilling. Replace that coin with a new penny worth a fifth of a shilling and decimalisation has occurred naturally.
I was five when this happened, and still remember grown-ups complaining bitterly. The old coins did have a certain weight to them, both historic and physically. When the pound coin was introduced people complained again. The strangest thing to me was the difference in size of the bank notes - £20 was flamboyantly larger than the pedestrian £1 note, it seemed huge.
Huge notes always remind me of Bresson's Pickpocket - a decade earlier but close enough [2].
[1] https://en.wikipedia.org/wiki/Bank_of_England_%C2%A320_note#... [2] https://www.youtube.com/watch?v=e0IcoDkGOmM
https://www.sec.gov/rules/other/decimalp.htm
True but punts were the currency in circulation until the start of 2002.
That's a nice read especially the older people being reunited with the old coins.