Lastminute.com has enjoyed its status as a dot.com star but a series of system failures could knock the gloss off its success.

In the past two months several customers have discovered that money has been deducted from their account without them purchasing any travel or gift products from its website.

Charlotte Brett, a London-based customer, was one of 80 Lastminute.com customers who suffered transaction problems with the internet firm. She said that in January and February £50 was deducted from her account on three occasions by the online travel agency even though she had not made a purchase.

The money was recredited to her account but Ms Brett claimed this took four weeks and was only done only after she alerted the company to the problem.

"I'm a very angry customer," Ms Brett said. "In my experience they have failed on the three most key areas - technology, customer service and internet capability."

Brent Hoberman, the chief executive of Lastminute.com, said the problems were caused by its third-party credit authority firm. He said the money had been refunded as quickly as possible and customers affected offered gift vouchers. "We did everything possible to remedy the situation," he said.

Lastminute's spokesman, Ian Jones, apologised to Ms Brett, explaining the flaw was being investigated. But Ms Brett said he failed to address why the money had been deducted without any purchase being made.