The currency is Sterling or Gibraltar Pounds which is a par with Sterling. Euros are accepted in certain shops in town you may be given the change in sterling. Gibraltar issues its own coins and banknotes - the coins are exactly the same size as equivalent UK coins (but are not valid for the use in the UK).

There are three of the main UK high street banks - Natwest, Barclays and Royal Bank of Scotland.  Three building societies Norwich and Peterborough, The Leeds and Newcastle Building Societies.  There are other private banks including Lloyds Bank Offshore, SG Hambros, Credit Suisse and Jyske Bank amongst others.  Several ATMs in town.  

Be warned that the exchange rate between Euros and sterling in shops and restaurants is a rip off so if paying by Euros you may be surcharged by as much as 50%.  Check your change including bank notes as you may receive Gibraltar currency thinking it's UK and once over the border it's too late. Some ATMs WILL issue Gibraltar pounds and not sterling so read the ATM small print carefully.

A good suggestion if you need spending money is to withdraw sterling at an ATM and keep your Euros in your purse. You can always take unused sterling home ( if you are from the UK ).