Intelligent Finance, the online and telephone bank owned by HBOS, suffered extensive online downtime on Sunday and Monday after a routine hardware upgrade ran into problems.

The downtime left customers unable to access their accounts or use any other part of the site for much of Sunday and Monday. The website was down from midnight on Sunday morning until 5:30pm that day, and from 9:45am on Monday right through until 5:20am on Tuesday morning -- 37 hours in total, spread over three days.

Problems arose when the bank was performing a hardware upgrade that included the addition of new servers, according to an IF spokesperson.

She said Sunday’s upgrades were long planned, and that the day had been chosen because traffic on the site was generally “not as intense”.

But the work carried out on the Sunday did not go to plan and affected customers attempting to use the service on Monday morning, with pages not loading properly. The system was taken offline again on Monday afternoon to reinstall the upgrade.

It is not the first time the bank’s website has been knocked out. In late 2002, some customers complained of being offline for up to five days.

IF defended its record of customer service. “Like any business we have to upgrade," said a spokesperson. “As a ‘telenet’ bank we are lucky that customers were able to deal with us on the phone too.”

Systems downtime remains a big problem among UK businesses, whether the customer-facing parts are affected or not. According to a recent poll, more than 80% of CIOs, IT directors and IT managers in large and medium-sized businesses worldwide saw business continuity as a priority for increased spending this year.

And Google suffered its own high profile downtime at the weekend when its analytics service went down between Saturday and Monday.