Why working in foreign currency on the purchase ledger, does the list of supplier balances never equal the creditors account on the balance sheet ?

Hello Lizard186.

Welcome to the Community page, 

This could be and most probably because of the exchange rates on the foreign currency. You can revalue the currencies and see if this resolves the differences you are seeing on the reports. 

To revalue the currencies is if you go to the main cog wheel> under lists>currencies>under action on the right-hand side is a drop-down arrow on the currency>click revalue currency.