Cannot comment on predecimal UK silver coins as they have all changed size. However Australian silver coins florin, shilling and sixpence still remain in the same format as the old imperial coins. With the florin now 20 cent, shilling 10 cent and sixpence 5 cent.
However sovereigns and half-sovereigns are deemed to not be legal tender for some reason although sovereigns etc. were minted in Australia at Sydney, Melbourne and Perth. because of this they attract a 10% GST (VAT). Pure gold coins do not attract GST.