Some Yorkshire Bank and Clydesdale Bank customers have experienced problems with using their debit cards today after the banks' systems operations were transferred to an external contractor at the weekend.

The problems were first reported on Sunday morning from 10:30 GMT, while the system operations of the two banks – which are part of the National Australia Bank – were being transferred. Yorkshire Bank declined to reveal the name of the external contractor that was taking over the systems.

However, it told the Press Association that it was experiencing problems with MasterCard debit transactions, and that it was working with merchant processing service provider and "partner First Data", which operates its network, to resolve the issue.

A spokesperson for Yorkshire Bank said: "There was a short service interruption at lunchtime today, which impacted some customer transactions.

"Service was restored by 1pm and continues to operate normally. This follows work to resolve any remaining problems caused by the debit card service disruption on Sunday."

The banks apologised for the issues and said that it will investigate any related claims on a case-by-case basis.

The direct debit problem is not the first IT problem that the banks have experienced in recent years. In 2010, a software update error caused thousands of Clydesdale Bank and Yorkshire Bank customers to make incorrect payments on their variable-rate mortgages.