WI Britain never decimalised its currency, instead keeping the traditional divisions of the pound:
1 pound = 20 shillings (1 shilling = 5p OTL)
1 shilling = 20 pence (1 penny = 0.416p OTL)
1 penny = 4 farthings (1 farthing = 0.10416p OTL)
coins used up to 1971 (pre-decimalisation)
"silver"
crown = 5 shillings (25p after 1971) - usually issued to commemorate special occasions - same size as today's 5 pound commemoratives
half crown = 2.5 shillings (12.5p) - still large and heavy
florin = 2 shillings (10p) - somewhat large and heavy
shilling (5p) - about the size of todays 10p
sixpence = (2.5p) - about the size of todays 5p
brass
threepence = (1.25p) - about the size of today's 20p, 12 sided
copper
penny = (0.416p) - very large and heavy
halfpenny = (0.2083p) - about the size of today's 50p, round
obsolete
farthing = (0.10416p) - not used after 1954, about the size of today's 1p