NatWest branchBank customers face further chaos as NatWest extended its trading hours once again to cope with the fallout from a computer failure almost a week ago.

Around 1,200 branches opened for the first time on a Sunday as staff battled to deal with a backlog of payments following Tuesday's IT glitch.

The debacle has rolled into a seventh day after parent company RBS said it was still experiencing technical issues and admitted some online services were unavailable.

The fiasco - also affecting RBS and Ulster Bank - continues to spark anger with customers apparently unable to access internet banking.

During the past week, clients have seen payments to go awry, holiday and home purchases interrupted and wages have appeared to go missing.

NatWest has more than 7.5 million personal banking customers but it remains unclear how many have been affected.

More than 1,000 NatWest branches are opening their doors from 8am to 7pm as staff seek to resolve the problems.

Susan Allen, director of customer services at RBS Group, insisted that progress was being made and expressed cautious optimism that RBS and NatWest customer account balances would be largely "back to normal" at the start of the working week.

"The knock-on effects of this technical failure mean there will be bumps in the road," she said. "We will do everything we can to minimise further disruption to our customers."

Stephen Hester, chief executive of NatWest owner RBS, has issued a public apology for the chaos and conceded the bank had let down its customers. His attempt to reassure clients followed mounting fears that thousands of people could be hit with penalty charges if their regular payments - including mortgages - were affected.