This discussion is taking me back to my year in London as a young coin collector, 1971-72. An odd mix of old system and new decimal coins were in circulation:
decimal half penny (long gone), decimal penny, decimal 2p, old sixpence (worth 2 1/2 new pence), decimal 5p, old shilling (worth 5p), decimal 10p, old florin (two shillings) worth 10p, decimal 50 p.
Anything bigger than 50 p was paper money (but as a 9 year old, in an economy where a Cadbury bar cost 5p, I didn't see paper money very often -- a pound was a lot of money then).
The decimal 2 p, 5 p and 10 p were much bigger than their modern versions. The other predecimal coins (half penny, penny, 3d, and half crown (2 shillings 6 pence)) that had circulated in the 1960s had been demonetized already.
The big prize was finding an old real silver sixpence, shilling or florin; that is, before 1947. They were not common but they did turn up in your change occasionally, going back to George V -- oldest I remember getting was a 1915 shilling. The base metal sixpence, shilling and florin coins dated 1947-1968 were still more common than their new decimal equivalents.