Silver is currently about £21 a troy ounce - £252 per troy pound. That makes a silver penny - 1/240th of a pound - worth about £1.05, or in old terms, a guinea. If the world goes into financial meltdown and paper currency as valuable as woodpulp, we may yet still see silver and copper making a comeback. The old penny was 9.4g - and with copper prices at about £5/kg worth nearly 5p - or a shilling in old money. 240 copper pennies are worth £11.28, not far off the metal price of 10 silver guineas.
Oh well, I'm sure we'll work it all out if it happens, and the youngsters will have to get used to £4-10/6d and suchlike.