Acting prime minister Julia Gillard says homeowners unhappy with their current interest rate should shop around for a better deal.

Ms Gillard has told Fairfax Radio this morning that treasurer Wayne Swan was working hard to put "competitive pressure" on the banks.

"We know that there’s a problem and people get locked into their mortgage and then they face these increases," she said.

"We want them to be able to shop around; we want them to be able to change banks. We want them to be able to say to their current bank: ‘unless I am being treated properly, I am off to another bank’."

"My message to Australians who hold mortgages – I am certainly an Australian with a mortgage - if you think you are getting a dud deal from your bank then shop around."

She said the prospect of losing customers was enough to make banks behave better.

The interim swapping arrangements would become permanent in November, the acting PM told host Neil Mitchell.

The interview with 3AW was prompted by the news that the National Australia Bank has increased its mortgage interest rate ahead of an official rise by the Reserve Bank.