Microsoft has confirmed that customers in Europe will not be able to easily upgrade Windows XP or Vista computers to the new Windows 7 operating system.

In the past there have been two ways to install new versions of Windows: a ‘clean’ installation, where the hard disk is wiped clean first, and an ‘upgrade’ installation. Performing an upgrade installation would allow users to keep their documents and programs in place.

However, this option will not be available when installing the European version of Windows 7, known as Windows 7 E.

Microsoft’s John Curran said that “for technical reasons we will only be able to offer Windows 7 E as a full version”.

The company’s Mike Ybarra told the US website Engadget the company was concerned about the problems that might be caused by removing Internet Explorer during an upgrade.

“We don't want to break anyone else's software, we don't want to break our own software,” he said.

To avoid losing files, users will need to copy all their documents to another storage device before installing Windows 7.

After installation, they can be moved back. A notice on the company’s website warns that “Whether your PC is running Windows Vista, Windows XP, or another operating system, E editions of Windows 7 require a custom (clean) installation. A custom installation does not preserve your files, settings, and programs.

"So, before installing E editions of Windows 7, make sure to back up your files and settings to an external hard disk, USB Flash drive, or other media.”

Computeractive will publish a full guide to this process when Windows 7 launches.