Math in the UK

While on a country walk some children asked my if I would like to buy some conkers.  Translation: horse chestnuts.  They are used in a game where kids thread the conkers onto strings and then take turns hitting each other's conker until it breaks. ( I'm sure they hit each other with them as well).   I was about to ask them if they were saving the money for something special when I noticed the sign:

That's right folks!  Buy your conkers here!!  5 for 5 pence, 10 for 20 pence, o  for a short time only 40 for a £1!!!

Britain's future businessmen:

(Don't worry the dad said I could take their picture)