The Inland Revenue is printing off Internet-filed self-assessment tax returns and rekeying the data into its existing systems.
The admission is the latest embarrassment for the Revenue and its IT outsourcer EDS, in their on-going struggle to make the online tax filing system work.
It also raises questions about the Inland Revenue's claim to be at the forefront of the drive towards e-government and could cause potential legal problems if errors are introduced during rekeying.
The Revenue said that any problems with the system, which went live last week, could result in the Internet filing site being taken offline or could even disrupt existing systems "with possibly serious impacts on local offices".
Staff have been told data received online will not automatically be transferred onto the Cesa system (the main self-assessment computer system) "for the first few weeks or so".
"Instead, we are printing them off and then keying them in through Local Data Capture," the Revenue said. "We are doing this so we can provide an Internet service to our customers at the earliest possible date and reduce risk."
The Revenue told Computer Weekly this approach is "commonly used by the big Internet trading sites when they first start out".
However, Alexander Drobik, vice-president of e-business at analyst group Gartner, was unimpressed with the explanation of what he dubbed "swivel chair technology".
"It is not uncommon, but that doesn't mean it is a great thing to do. It is the result of a project not being done properly," said Drobik.