Hi Rob,
although you can use ATM's with your NatWest account and soon even pay through direct debit ( new EU bank regulation) if you work in Malta you will probably be paid by cheque that you will need to pass into your bank . And using any other bank services (loans,buying real estate, paying with debit card and so on) will be better or cheaper with a local bank.
It can be easy or difficult to open a bank account in Malta so a standard recommendation from your UK bank will help you set up a new account.
The biggest public banks in Malta are HSBC and BoV with branch offices in all major localities.