If you want to know why we changed try to make sense of Bellringers explanation and then try to add up say 2 pounds 5 and sixpence, 1 pound 3 and tuppence, eighteen bob and see what change you should get from a fiver.
I think the answer's half a packet of mangle-worzells or something.
Anyway despite the fond rememberances of a few of the older generation who have trouble accepting change it was clearly a ridiculous system that had just evolved over hundreds of years and had reached the end of it's life and needed to go and join groats and the like in that great accounting house in the sky.
Now if we can just do the same with inches, pounds, acres, furlongs, chains, leagues, fathoms, poles, pounds ounces....
To look at English counting systems anybody would think we elvolved with 12 fingers