I never, ever, understood the nonsense of any decimal coinage that started with a half penny.
They replaced the easily understood historic currency of pounds, shillings and pence with a unit of currency based around multiples of ten - but retained the half-penny.
Keeping a smallest coin close in size to the old penny was seen as essential, to avoid driving price changes. The halfpenny was always going to be lost, which was already being seen as pushing up prices.
So the choice was between a primary unit of £1 with half pence, or a 10s unit without. I thought at the time that the latter was a better idea, as it meant 1s became 10np, and that made conversion from shilling amounts easier. My logic was that those people whose limited numeracy meant any change would be difficult did almost all of their transactions in shillings not pounds. Remember that, at the time, prices up to £5 were commonly quoted in shillings.
I was very surprised when I saw Jim Callaghan explaining on TV, with a straight face, why they chose the £1 option on the grounds it made conversion easier! (That would have been in 1966.) Of course it was really to please those in the City who worried that changing the pound for something else - it would need a new name - would risk confidence in Sterling.
Incidentally, my father was part of a project team to computerise the Post Office Savings Bank, starting work while the decimalisation plans were still being worked on. They chose to use a base unit of £1/1200, converting £sd amounts into multiples of that during the initial transfer. Conversion to an effective base unit £1/200 and then £1/100 was done later on, and could be explicitly based on a policy decision.