Complex sentence: The rating was 6 pence higher than the actual silver content of the coins should have allowed in order to keep the coins in circulation as there was no advantage to melting the coins for their bullion content.
Split into simpler sentences: The rating was 6 pence higher than the actual silver content of the coins should have allowed. This was done in order to keep the coins in circulation as there was no advantage to melting the coins for their bullion content.