Poland has announced that it will make the European single currency, the euro, the main reference for the exchange rate of its money, the zloty.

The central bank said that from the first of January - the day the single currency is launched - 55% of the value of the zloty will be determined by the value of the euro and the rest by the value of the dollar.

The BBC business reporter says many other countries around the world who hold European currency reserves - such as French francs or German marks - will also be replacing these with the euro.